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P BAND

The P band is the frequency band from 225 to 390 Mhz employed in radar.
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P-80 SYSTEMS

P-80 systems are an American bulletin board (BBS) and CD-ROM supplier specialising in pirated computer software (warez) for the PC and also information on computer hacking, phreaking and other illegal activities.
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PACHOMETER

A pachometer or pachymeter is an instrument used for measuring thickness such as the tickness of the glass of a mirror, or the thickness of paper.
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PACKET

In the sense of communications, a packet is a structured group of binary digits in a prearranged sequence containing synchronism, address, control an error-checking data. Specialised synonym for a 'block' of data in CCITT Packet Data Network standards.
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PACKET SWITCHED NETWORK

A Packet Switched Network is a network dedicated to the routing and delivery of data put in the form of standardised 'packets.'
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PACKET SWITCHING

Packet Switching is the technique in which a stream of data is broken into standardised units called 'packets,' each of which contains address, sequence, control, size and error checking information in addition to the user data. Specialised packet switches operate on this added information to move the packets to their destination in the proper sequence and again present them in a contiguous stream.
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PADSAW

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A padsaw or pad saw, is a small handsaw consisting of a narrow blade inserted into a handle, and used for cutting holes.
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PAEONINE

Paeonine or red coralline is an artifical red nitrogenous substance used as a dye. Paeonine is obtained by heating phenol with sulphuric and oxalic acid . It is used for dyeing silk and wool, and is also printed upon cotton.
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PAGEMAKER

PageMaker was formerly a very popular, easy to use, WYSIWYG desktop publisher that allowed the design, layout, and production of typeset-quality documents on the Macintosh and PC running Windows. The product, one of the first desktop publishers for the Macintosh, provided a comprehensive set of tools for integrating text and graphics from virtually any Macintosh application into a professional-looking document. Nearly identical to PageMaker for the PC, this program offered user-defined style sheets, automatic text flow through a document, and 20 design templates. Rather than using a grid approach, PageMaker worked like a paste-up board on which to define the placement of elements on-screen after defining the number of columns the document will have.

PageMaker had a wide range of uses, from the occasional quick memo and graphics based publication, to a complex, content-oriented document with graphics (it was used to typeset the magazine Here's Health during the early 1990s). It was ideal for an environment using both PCs and Macs because a version was available for each machine and files could be transferred between the two environments.

When PageMaker was run a blank page was seen on-screen. Text and graphics could be imported using a place command to position the material as it was to appear on the printed output. The product retained formatting from word processing files such as tabs, type styles, justification, and proportional spacing. PageMaker had a built-in text editor which could also act as a basic word processor. Changes made in PageMaker were automatically reflected in the word processing document. The program automatically flowed text throughout the document and wrapped text around graphics. Its editing features controlled text size, style, typeface, multiple columns, and automatic hyphenation. Imported graphics could be sized, scaled, and cropped on-screen. Rules and line styles helped to position graphic images and text, and allow easy creation of boxed text, headlines, and framed images. Ruler guides controlled layout and column guides assisted in the actual placement and margins of graphics and text. PageMaker allowed the creation of style sheets. Users could see and work with multiple views of a page layout or two pages at once so that a double-page spread could be designed.
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PAGING-MACHINE

A paging-machine was a machine for printing consecutive numbers on the pages of a book, bank-notes and cheques, railway-tickets, etc. Several machines of this kind were invented, all of which consisted essentially of a number of revolving discs bearing the ten digits in raised figures on their circumference, with various contrivances for making the first disc describe one-tenth of a revolution after every figure is printed, for making the second disc describe one-tenth of a revolution every time the first makes a complete revolution, and so on, as well as for supplying the figures with ink at each impression. Provision was also made for the printing of duplicate and alternate numbers if this was required.
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PAINT

Paints are mixtures of dry powder colours (pigments) with an oil or varnish vehicle. There are a number of classes of paints, for example those used for painting and decorating houses are much coarser than those used in the fine arts.
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PALAEOGRAPHY

Palaeography is the study of ancient manuscripts written on papyrus, parchment or similar material, as distinct (since later times) from epigraphy which is the study of ancient inscriptions incised on hard materials such as wood, stone or metal. It is wider than diplomatics, which deals with the written sources of modern history.
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PALAEONTOLOGY

Palaeontology is a branch of biology and geology which deals with fossils. It is divided into palaeozoology and palaeobotany, which respectively have animals and plants as their subject matters.

The comparison of the fossil remains of plants and animals, belonging for the most part to extinct species, gave a powerful impulse to the science of comparative anatomy during the 19th and early 20th centuries, and through it a truer insight was obtained into the natural arrangement and subdivision of the classes of animals. But the science which profited most from palaeontology was geology.

Palaeontology, apart from its importance as treating of the past life-history of the earth, assists the geologist in his determination of the chronological succession of the materials composing the earth's crust. As a general result of united geological and palaeontological researches, it was found possible to divide the entire series of stratified deposits into a number of rock-systems or formations, each of which is defined by possessing an assemblage of organic remains which are not associated in any other formation. These systems as a whole are divided into three great divisions, based on the characters of their organic remains, and thus representing three successive life-periods, as follows : Palaeozoic, or ancient life epoch, which includes the Laurentian, Cambrian, Silurian, Devonian, Old Red Sandstone, Carboniferous, and Permian rock systems. Mesozoic, or middle life epoch, including the Triassic, Jurassic or Oolitic, and Cretaceous rock systems. Cainooic, or recent life epoch, which comprises the Eocene, Miocene, Pliocene, and Post-tertiary rock systems. The fossil remains of the first two divisions mostly belong to extinct species. The Cainozoic fossils belong mostly to living species or species only recently extinct.
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PALLADIUM

Palladium is a rare grey-white metal element with the symbol Pd, discovered by Wollaston in 1803. Palladium is found in small quantity associated with native gold and platinum. It closely resembles platinum, but is harder, lighter and more easily oxidised It has the power of absorbing a very large amount of hydrogen to which it is permeable when heated. It is used in an alloy with gold in dentistry and jewellery. In its pure form it is used for making watch springs and mirrors and scientific instruments and for absorbing hydrogen.
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PALM KERNEL OIL

Palm kernel oil (palm oil, palm butter) is a fatty oil obtained from several species of palms, but chiefly from the fruit of the oil-palm, or Eloeis guineensis, a native of the west coast of Africa. This tree grows to the height of 80 feet, bears a tuft of large pinnate leaves, and has a thick stem covered with the stumps of the stalks of dead leaves. The fruits, which are borne in dense clusters, are about 1.5 inches long by 1 inch in diameter, and the oil is obtained from their fleshy covering. In cold countries it acquires the consistence of butter, and is of an orange-yellow colour. It is employed in the manufacture of soap and candles, for lubricating machinery, wheels of railway-carriages, etc. By the natives of the Gold Coast this oil is used as butter; and when eaten fresh is a wholesome and delicate article of diet.
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PALMITIC ACID

Palmitic acid is a widely distributed naturally occurring fatty acid present in palm oil, with the formula C16H32O2. It exists partly in a free state but generally in combination with glycerin (as a glyceride). It forms a solid, colourless, inodorous body, which melts at 62 degrees Centigrade.
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PANASONIC RF-B60

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The Panasonic RF-B60 was a portable scanning radio introduced around 1987. The
Panasonic RF-B60 covered 522 khz to 1611 khz, 1615 khz to 29.999 Mhz in AM mode and 87.5 Mhz to 108 Mhz in FM wide mode.
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PANNOMITE

Pannomite is a coal-mining explosive comprised of nitro-glycerine, collodion cotton, ammonium nitrate, dextrin, glycerine, nitrotoluene and alkali chloride.
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PANTHENOL

Panthenol (Pro vitamin B5) is the alcohol analogue of pantothenic acid. Whilst its vitamin properties are not proven in cosmetics and toiletries, it does have pronounced moisturising properties and gives and excellent ' skin feel' to products containing it.
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PANTOGRAPH

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A pantograph is an instrument for mechanically tracing a figure similar to a given figure, but enlarged or diminished in a definite ratio. It consists of four rods forming a jointed parallelogram, with sides continued to convenient distances beyond the joints.

In railway terminology, the name pantograph is applied to an articulated framework resembling a parallelogram used to collect electrical power from overhead power cables.
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PANTOTHENIC ACID

Pantothenic acid is a hydroxy acid found in plant and animal tissues that is one of the vitamin B complex of substances and is used for cell growth.
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PAPAIN

Papain is a substance found in the juice of papaw. It has an identical action to Trypsin.
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PARA-AMINOBENZOIC ACID

Para-aminobenzoic acid is an acid found in yeast and in liver. It is used in the manufacture of dyes and pharmaceuticals.
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PARA-CRESOL

Para-cresol is a cresol found in bad eggs.
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PARABOLA

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A parabola is a curve, any point of which is equally distant from a fixed point, called the focus, and a fixed straight line, called the directrix.

The term parabola is also applied to any curve having an infinite branch, without having a retilineal asymptote.
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PARABOLOID

A paraboloid is a solid figure made by the revolution of a parabola about its axis.
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PARACHUTE

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A parachute is a rectangular or umbrella-shaped apparatus that allows a person or load attached to it to descend slowly from a height, especially from a balloon or aeroplane. The first human parachute descent was made in 1797, when Jacques Garnerin parachuted from a balloon over Paris. Folding parachutes were first used in America in 1880, and towards the end of the Great War aviators first used parachutes to escape from their aeroplanes. Early parachutes were made of canvas, and later silk. Modern parachutes comprise many separate panels of nylon, so that tears are confined to a small area. Until recently parachutes were umbrella-shaped, but parafoils (air-filled aerofoils) are now common. In addition to their use as safety devices, parachutes are used for sport, for aerial drops of supplies and equipment, and as braking devices (drogues) for landing aircraft or other vehicles.
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PARADICHLOROBENZENE

Paradichlorobenzene is a white crystalline, volatile substance which is insoluble in water of the benzene series. It has a penetrating odour and is used chiefly as a moth repellent.
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PARADOX

Paradox 3.0 was a relational database manager from Borland International, that, the manufacturers claimed, stuck a balance between functionality and ease of use. It offered the power of many of the advanced database products, yet was easy enough for the novice to use. It included enhanced relational operations, presentation-quality graphics, crosstab views, and enhanced query-by-example operators.

Paradox appealed to a wide range of users because it had menus as well as a programming language. The menus, which resembled the popular Lotus 1-2-3 interface, provided advanced capabilities to the beginning user, while the command language, Paradox Application Language (known as PAL), allowed sophisticated users to create complex turnkey systems and custom applications. PAL provided all the functions of competitive database programming languages. For those who used PAL to develop applications, Paradox also included an application generator that created PAL code which could be edited.


Paradox employed the artificial intelligence technique, query-by-example, to let users make multiple-file queries and database manipulations by giving an example of the kind of data wanted.
Paradox also used artificial intelligence to speed up queries by searching for the best path. Any index which Paradox created to answer a question would be used to answer a later query when appropriate. Paradox's multiforms capability allowed users to display records from multiple tables within a form and create forms with scrolling regions without any programming.

Paradox supported a multitable feature in its reporting capabilities. The most visual feature was the ability to create presentation-quality colour graphics such as pie charts, line, bar, and XY graphs. An automatic lookup function allowed the user to fill entire records just by filling in one field. This feature was excellent for creating invoices that automatically entered customer information on the invoice based on the entry of a customer number. As long as two files had a common field, information could be shared between them. This standard relational database feature enabled the user to have small manageable files instead of files that were cumbersome and difficult to work with. When searching for specific information, the user simply checked off the fields they wanted to see in the answer table.
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PARAFFIN

Paraffin is a colourless, tasteless, odourless, solid fatty family of hydrocarbons produced from the dry distillation of coal, shale, lignite, peat and the like. Refined paraffin is largely manufactured into candles, which may be either white or coloured, and may be mixed with a certain quantity of wax, etc. The liquid oils obtained in the process come into commerce under the general name of paraffin-oil, the lighter oils being used for illuminating and the heavier for lubricating purposes.In Britain the term paraffin is often incorrectly applied to kerosene.
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PARALLAX

The term parallax describes the apparent movement of an object when viewed from two different positions.
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PARALLEL MOTION

Parallel Motion is a mechanical contrivance employed by Watt to communicate the alternate pushes and pulls of the piston-rod of a steam-engine to the end of a vibrating beam, and which prevents the action of forces tending to destroy the right-line motion of the piston-rod. The motion given to the end of the rod is not accurately in a straight line, but it is very nearly so. Watt's parallel motion is still employed in all stationary beam-engines. In marine beam-engines the arrangement employed differs somewhat in form, but is the same in principle as Watt's contrivance.
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PARALLEL TRANSMISSION

Parallel Transmission is the simultaneous transmission of all parts of a signal at one time; in data transmission, requiring a separate signal path for each of the bits of a character; internal to computers, this is called a 'parallel bus.'
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PARALLELOGRAM

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A parallelogram is a quadrilateral (four-sided) figure, whose opposite figures are parallel, and consequently equal, but whose angles are not right angles.
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PARALLELOGRAM OF FORCES

The Parallelogram of Forces is an important dynamical principle, deduced by Isaac Newton, which may be stated thus: If two forces acting in different directions on a particle at the same time be represented in magnitude and direction by two straight lines meeting at the particle, their resultant effect in giving motion to the particle is that of a force represented in magnitude and direction by the diagonal (terminating in the particle) of the parallelogram, of which the two former lines are two sides.
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PARALLELOPIPED

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A parallelopiped is a regular rectangular solid figure whose faces are parallelograms.
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PARALLOGRAM

A parallogram is a quadrilateral whose opposite sides are parallel.
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PARAXIAL

In physics paraxial is an adjective describing a light ray as being parallel to the axis of an optical system.
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PARIS GREEN

Paris green is an insecticide based upon the pigment emerald green.
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PARITY

In communications systems and computers, parity is a constant state of equality; one of the oldest and simplest methods of error checking data transmission. Characters are forced into parity (total number of marking bits odd or even as selected by choice) by adding a one or zero bit as appropriate when transmitted; parity is then checked as odd or even at the receiver.
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PARITY BIT

A Parity Bit is a check bit appended to an array of binary digits to make the sum of all the digits always odd or always even.
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PARITY CHECK

Parity Check is a checking method that determines if the sum of all the digits in an array is odd or even.
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PARKED DOMAIN MONETIZATION

Parked domain monetization is the business of purchasing world wide web domain names and using them to display advertising on the home page so as to earn revenue from the traffic that accidentally results at the domain. The traffic to these web sites comes from a variety of sources, but is mainly from people miss-typing the name of a well known web site when attempting to access it. At the end of the 20th century, and the start of the 21st century when the world wide web became very popular, unscrupulous individuals realised they could intercept traffic intended for popular web sites by registering variations of the web site's name, and could then display advertising to the unwitting viewers of these web pages. This quickly resulted in many thousands of variations of popular web sites names being registered and directed to single pages containing nothing but advertising.
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PARSEC

A parsec is an astronomical unit of distance equivalent to 3.2616 light-years.
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PARTICLEBOARD

Particleboard is the American term for what the British call chipboard. That is a cheap substitute for timber made from wood chips glued together and frequently used for kitchen worktops, low grade furniture and flooring.
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PASC

PASC is an abbreviation for Precision Adaptive Sub-band Coding, and is a digital audio encoding method effectively the same as MPEG layer 1 and was used in Philips now defunct Digital Compact Cassette system. PASC divides the digital signal into equally spaced sub-bands and compresses the data to about 1/4th of the original size)
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PASCAL

Pascal is an Algol-descended computer programming language designed by Niklaus Wirth on the CDC 6600 around 1967 as an instructional tool for elementary programming. The language, designed primarily to keep students from shooting themselves in the foot and thus extremely restrictive from a general- purpose-programming point of view, was later promoted as a general-purpose tool and, in fact, became the ancestor of a large family of languages including Modula-2 and Ada.
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PASCAL'S PRINCIPLE

In physics, Pascal's principle states that when a fluid completely fills a vessel, and a pressure is applied to it at any part of its surface, that pressure is transmitted equally throughout the whole of the enclosed fluid.
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PASSBAND TUNING

In radio terms, passband tuning is a circuit that allows the operator to move the selectivity bandwidth of the receiver above or below the frequency to which the radio is tuned. This is often helpful in reducing interference.
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PASSOMETER

A passometer was a small machine, with a dial and index-hands like a watch, carried by pedestrians to record their steps in walking; a sort of hodometer.
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PASSWD

In Linux computer systems passwd is an ASCII file that contains a list of the system's users and the passwords (in an encrypted format) they must use for access. The /etc/passwd file is comprised of lines, each containing a single entry. Each line has the format:

login name:passwd:UID:GID:user name:directory:shell

Where login name is the name of the user on the system. password is The encrypted optional user password. UID is the numerical user ID. GID is the numerical group ID for this user. user name is the optional comment field (often containing a full username), directory is the user's $HOME directory, shell is the program to run at login (typically if this field is empty the computer will use /bin/sh).
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PASSWORD SHADOWING

Password shadowing is a UNIX computer security system where the encrypted password field of /etc/ passwd is replaced with a special token and the encrypted password is stored in a separate file which is not readable by normal system users. On older systems,
password shadowing was often defeated by using a program that made successive calls to getpwent() to obtain the entire password file.
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PASTEL COLOURS

Pastel colours are colours in which the purity has been reduced by the addition of grey.
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PAWL

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A pawl is a short bar which works in conjunction with a ratchet-wheel to prevent backward rotation of the wheel.
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PC PAINTBRUSH

PC Paintbrush by ZSoft is a good drawing program that supports high resolution VGA graphics. It is a full-featured colour-painting program that lets you create and edit freehand illustrations at the pixel level. It supports a wide range of popular scanners allowing scanned images to be imported and edited in black and white, 16 shades of grey, or in colour. Painting elements include boxes, circles, rounded boxes, curves, lines, and text. All of the objects can be sized and filled. The standard painting tools such as a paintbrush, paint roller, eraser, and spray can are available as well as more unique tools such as a colour eraser which lets you erase a single colour in a defined area. When linked to a scanner, a special menu is available that lets you select items to adjust your scanner capabilities. This program lets you paint, scan, and edit images at 300 dpi in colour or with 16 levels of grey. Images can be scanned in and resized without losing picture qualify. PostScript output devices are supported.
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PC/FOCUS

PC/Focus by Information Builders, Inc. is a complete, fourth-generation language database and information management system for personal computers. Its design, function, and capabilities are identical to its big brother Focus, one of the leading information centre products for IBM or compatible mainframes. Code that is written for one version is easily transported to the another. Since mainframe Focus and PC/Focus share a common language, PC/Focus can be used to prototype mainframe Focus applications. This method is much less time-consuming frees up valuable mainframe resources. PC/Focus supports a menu-driven user interface based on Information Builders Talk Technology which accesses most PC/Focus commands from a menu. The PC/Focus Windows facility lets you incorporate the programs menu interface into customised applications. The scripting or macro language lets programmers store communications procedures that can automatically execute dial-up sequences for accessing remote systems. A screen painter and report generator
make it much easier to design your applications. Database maintenance procedures can be automated by using ModifyTalk which generates procedures based on answers that you give to a series of questions concerning the fields you want to modify. The product supports a SQL Translator which enables the user to type SQL requests against a mainframe Focus database.
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PCANYWHERE

pcANYWHERE III is a menu-driven remote control program for IBM PC-compatibles that allows the user to control and/or monitor one PC from another over a communications link. Suitable for support purposes and typically used with standard dial-up modems, pcANYWHERE III connects two PCs so their screens and keyboards are linked as one. Whatever the remote user sees on-screen is also seen on the local screen. pCANYWHERE III includes both host and remote portions necessary for remote connection of two PCs, and is useful for remote connection into networking environments such as Novell NetWare. The package includes a chat mode and call logging feature, and supports programs that require CCA, EGA, MCGA, VGA, and Hercules Graphics.

On the remote PC, pcANYWHERE III runs underneath other applications as a RAM resident program, occupying only 45K of RAM. The local portion runs as a primary task on a PC. The local PC supports any number of remote users and can he programmed with the appropriate telephone numbers and passwords so users can be called by selecting them from a pop-up directory window. The remote computer can be programmed to automatically call the support computer.
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PCM

In audio engineering, PCM (Pulse Code Modulation) is a scheme for encoding audio data as a series of pulses. Each pulse defines a transition from binary one to binary zero.
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PCMCIA

PCMCIA (Personal Computer Memory Card International Association) is a standard for miniturized laptop expansion cards for modems, storage, and other devices. Often called PC cards.
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PCOPY

Pcopy by Patri-Soft is an extension to the DOS computer operating system. Even with DOS 6.0, the DOS copy command can be dangerous to use and has limited options. Pcopy provides abundant options including: Multiple output disks, fill disks efficiently, split files across disks, select files by date/time/size and update/ merge directories. Pcopy includes a special *DISK*.* type wildcard.
Pcopy provides a facility to scan/make directories, prevent accidental file overlays. Pcopy includes both a menu and command line interface.
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PCSHIELD

PCShield by Axent Technologies Limited is a good practices enforcing software product for personal computers. It forces users to select passwords which are hard to crack, and provides encryption for data.
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PDEL

Pdel by Patri-Soft is an extension to the DOS computer operating system. It has extensive file selection capabilities letting you delete just what you want. You can select by date/time, size, attribute and special wildcard patterns like *DISK*.* and mode. You can delete until a specified amount of free space exists. Wipe file data before deleting to prevent file undelete. A test feature simulates delete. Pdel includes an emergency stop by pressing any key.
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PDP-1

The PDP-1 was the first product made by DEC, and was built to demonstrate the feasibility of building a fully-fledged stored-program computer from transistorised digital circuit modules. The PDP-1 was the first machine with random-access core memory to be sold for under $100,000 and was effectively the world's first minicomputer.
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PDP-10

The PDP-10 (Programmed Data Processor model 10) was a computer that made timesharing real. It was adopted in the mid-1970s by many university computing facilities and research labs, including the MIT AI Lab, Stanford, and CMU. The
PDP-10 was eventually eclipsed by the VAX machines (descendants of the PDP-11) when DEC recognised that the 10 and VAX product lines were competing with each other and decided to concentrate its software development effort on the more profitable VAX. The PDP-10 was finally dropped from DEC's line in 1983, following the failure of the Jupiter Project at DEC to build a viable new model.
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PDS

PDS is an abbreviation for Portable Diagnostic System. It is an expert system which diagnoses faults in machinery from information received from sensors connected to the machinery. Sensor readings are compared with known data about component malfunction symptoms to diagnose faults.
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PEAT

Peat is a fibrous organic compound found in bogs that is formed by the partial decomposition of plants in the acid water of the bog. Peat is a compact, dark brown organic material with a high carbon and represents the first stage in the transformation of vegetation into coal. Peat bogs are distributed throughout the world; extensive deposits are found in North America, Russia, the Scandinavian countries, England, and Ireland. Dried peat, often compressed into briquettes, is used in many European countries, particularly Ireland, as a fuel, although it is not as efficient as coal because of its large content of water and ash. Peat and commercial preparations of partly decayed vegetable matter that are also called peat have excellent moisture-retaining qualities and are used as mulching and soil-improving material for plants.
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PECTIN

Pectin is the name given to any of a group of complex carbohydrate derivatives produced in plants.
Pectins are white amorphous substances that yield a viscous solution with water; when combined in the proper proportions with sugar and acids, they form a gelatinous substance that is the thickening agent in fruit jams. Commercial pectin, obtained from apples or lemons, is used in preparing jam from fruits deficient in pectin.
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PEDOLOGY

Pedology is soil science, that is the study of the formation, nature and classification of soil. Modern pedology was founded by the Russian scientist, Dokuchaiev during the late 19th century. The general theory of soils as independant natural bodies was proposed by Dokuchaiev, developed further by Sibirtsev and organised by Glinka. The first international congress of soil science was held in the USA in 1937.
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PEDOMETER

A pedometer is a device used for estimating the distance travelled on foot by recording the number of steps taken by the bearer of the device.
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PEGASUS MAIL

Pegasus Mail is a free, standards-based electronic mail client for IBM PC computers, suitable for use by single or multiple users on single computers or on local area networks.
Pegasus mail is very feature rich, including mail filtering, mail-merge, and the ability to operate multiple-user accounts from one PC. Pegasus Mail can run on single computers using the DOS or Windows operating system, or on local area networks - it has special support for Novell NetWare LANs that allow it to operate intuitively and with almost no maintenance. The program also supports multiple users on a single computer. Versions are available for both 32-bit Windows (Windows 95, 98, NT4 and 2000) and 16-bit Windows (any version of Windows 3.1 or later). Pegasus Mail can act as a complete internal mail system on its own without needing further servers or components: it can send and receive Internet mail on its own using standard protocols (SMTP, IMAP and POP3).
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PELTON WHEEL

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The Pelton Wheel is a type of impulse turbine in which specially shaped buckets mounted on the perimeter of a wheel are hit by a fast-flowing jet of water, causing the wheel to turn. The Pelton wheel was invented by the American engineer L A Pelton around 1882.
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PENDULUM

In the widest sense, a pendulum is a heavy body suspended so that it is free to turn or swing upon an axis which does not pass through its centre of gravity. Its only position of stable equilibrium is that in which its centre of gravity is in the same vertical plane with the axis. If the body is displaced from this position it will tend to return to it, and it will oscillate or swing from one side of that position to the other until its energy is destroyed by friction, and it at length comes to rest. A small, heavy body suspended from a fixed point by a string, and caused to vibrate without much friction, is called a 'simple pendulum. When. the swings of a simple pendulum are not too great - that is, when they are never more than about 3 degrees on each side of the position of rest - the pendulum is isochronous, that is each swing occupies the same time.

The ordinary pendulum is what is properly a 'compound pendulum.' A compound pendulum, as seen in clocks, is usually a rigid, heavy, pendulous body, varying in size according to the size of the clock, but the 'seconds' pendulum may be considered the standard. The pendulum is connected with the clockwork by means of the escapement, and is what renders the going of the clock uniform. In a clock it is necessary that the period of vibration of the pendulum should be constant. As all substances expand and contract with heat and cold, the distance from the centre of suspension to the centre of gravity of a pendulum is continually altering.

Pendulums constructed so that increase or diminution of temperature do not affect this ratio are called compensation pendulums. These take particular names, according to their forms and materials, as the gridiron pendulum, the mercurial pendulum, &c. The former is composed of a number of rods so connected that the expansion or contraction of certain of them is counteracted by that of the others. The mercurial pendulum consists of one rod with a vessel containing mercury at the lower end, so adjusted in quantity that whatever alterations take place in the length of the pendulum, the centre of oscillation remains the same, the mercury ascending when the rod descends, and vice versa.
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PENTADECAGON

A pentadecagon is a fifteen-sided polygon.
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PENTAGON

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A pentagon is a five-sided regular polygon.
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PENTODE

A pentode is an electronic amplifying valve with five main electrodes.
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PENTOSE

A pentose is a sugar with five carbon atoms in the molecule.
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PENUMBRA

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A penumbra is the partial shadow between the full light and the total shadow caused by an opaque body intercepting the light from a luminous body, the penumbra being the result of rays emitted by part of the luminous body. An eye placed in the penumbra would see part of the luminous body, part being eclipsed by the opaque body; an eye placed in the 'umbra', or place of total shadow, would receive no rays from the luminous body; an eye placed anywhere else than in the penumbra and umbra sees the luminous body without eclipse. The subject is of importance in the consideration of eclipses. In a partial eclipse of the sun, as long as any part of the same is visible the parties observing are in the penumbra when the eclipse is total, in the umbra.
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PEPPER'S GHOST

Pepper's ghost is a method of producing the illusion of a ghost on the theatrical stage. A large sheet of polished plate glass placed diagonally across the stage acts as a mirror, but at the same time permits objects on the stage to be seen through it. An actor attired to represent the ghost is concealed in the wings and is strongly illuminated. All else surrounding him is painted or draped dull black so that an image of the actor only is formed by the plate glass. The illusion is rendered complete by the fact that light from objects on the stage behind the image causes the ghost to appear transparent. Headless ghosts result simply from enclosing the actor's head in dull black cloth.
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PERCHLORIC ACID

Perchloric acid (HClO4) is an acid prepared by the action of strong sulphuric acid upon potassium perchlorate. It is a colourless, syrupy liquid, resembling sulphuric acid. Brought into contact with organic matter it is instantly decomposed, often with explosive violence. The perchlorates have the general formula MClO4, where M represents a monovalent metal, such as potassium or sodium.
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PERDIT

Perdit is a former German mining, demolition, and rifle grenade explosive comprised of ammonium nitrate 76 per cent, potassium perchlorate 6 per cent, wood-meal 2 per cent, dinitrotoluene 16 per cent.
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PERIGEE

Perigee is an astronomical term referring to the position in the Moon's orbit nearest to the earth, opposite to Apogee.
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PERIHELION

The perihelion is that part of the orbit of the earth or any other planet in which it is at the point nearest to the sun. The 'perihelion distance' of a heavenly body is its distance from the sun at its nearest approach.
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PERIKON DETECTOR

A Perikon Detector was a form of crystal detector employed in the early days of radio broadcasting. It consisted of a crystal of zincite and a crystal of bornite so mounted that there was a point contact between them.
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PERIMETER

In geometry, the perimeter is the bounds or limits of any figure or body. The perimeters of surfaces or figures are lines; those of bodies are surfaces.
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PERIOD

In astronomy, a period is the interval of time occupied by a planet or comet in travelling once round the sun, or by a satellite in travelling round its primary.
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PERIODIC LAW

In chemistry, periodic law is the law that the properties of the elements are periodic functions of their atomic numbers.
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PERIODIC TABLE

In chemistry, the periodic table is a table illustrating the periodic system in which the chemical elements are arranged in the order of their atomic numbers are shown in related groups.
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PERISCOPE

A periscope or altiscope (formerly known as a polemoscope) is an instrument consisting of an arrangement of mirrors in a vertical framework, by means of which a person is enabled to overlook an object (a parapet, for instance) intervening between himself and any view that he desires to see, the picture of the latter being reflected from a higher to a lower mirror, where it is seen by the observer.
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PERL

Perl is an interpreted language optimised for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for many system management tasks. The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal). It combines some of the best features of C, sed, awk, and sh. Expression syntax corresponds quite closely to C expression syntax. Unlike most Unix utilities, Perl does not arbitrarily limit the size of your data - if you've got the memory, Perl can read in an entire file as a single string. Recursion is of unlimited depth. And the hash tables used by associative arrays grow as necessary to prevent degraded performance. Perl uses sophisticated pattern matching techniques to scan large amounts of data very quickly. Although optimised for scanning text, Perl can also deal with binary data, and can make dbm files look like associative arrays.
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PERMAID

Permaid is an expert system, developed at Honeywell for trouble shooting large disk drives.
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PERMALLOY

Permalloy is a nickel steel alloy, containing about 78 percent nickel. It is characterised by a very high permeability in low magnetic fields. It is extensively used in submarine cables.
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PERMANENT

When applied to pigments and stains, the term permanent means fast to light, that is that the pigment will not fade over time due to exposure to light.
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PERMANENT GREEN

Permanent green is a pigment comprising a mixture of viridian and either cadmium yellow or zinc chrome.
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PERMANENT WHITE

Permanent White is a white pigment consisting of barium sulphate precipitated from the chloride by adding dilute sulphuric acid.
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PERMANGANATE

A permanganate is any salt of permanganic acid. Sodium permanganate and potassium permanganate are used for the oxidation of compounds in organic preparations.
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PERMANGANIC ACID

Permanganic acid is a crimson, strongly acid solution used in analysis for the estimation of iron and oxalic acid.
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PERMUTATIONS AND COMBINATIONS

In mathematics the different orders in which any things can be arranged are called their 'permutations.' The 'combinations' of things are the different collections that can be formed out of them, without regarding the order in which the things are placed. Thus the permutations of the letters a, b, c, taken two at a time, are ab, ba, ac, ca, bc, cb, being six in number. Their combinations, however, are only three, namely ab, ac, bc; and so in all cases the number of permutations exceeds the number of combinations. The theory of permutations and combinations is of some importance from its bearings on that of probabilities.
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PERPENDICULAR

In geometry, perpendicular is a line falling directly on another line, so as to make equal angles on each side. A straight line is said to be perpendicular to a curve, when it cuts the curve in a point where another straight line to which it is perpendicular makes a tangent with the curve. In this case the perpendicular is usually called a normal to the curve.
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PERPETUAL MOTION

Perpetual motion is motion that, once originated, continues for ever or indefinitely. The problem of a perpetual motion consists in the invention of a machine which shall have the principles of its motion within itself, and numberless schemes have been proposed for its solution. It was not until the discovery of the principle of the conservation of energy, experimentally proved by Joule, that the impossibility of the existence of a perpetual motion was considered to be a physical axiom. This principle asserts that the whole amount of energy in the universe, or in any limited system which does not receive energy from without, or part with it to external matter, is invariable. But every machine when in action does a certain amount of work, if only in overcoming friction and the resistance of the air, and as the perpetual motion machine can start with only a certain amount of energy, this is gradually used up in the work it does. A machine, in short, would be required in which there was no friction, and which met with no resistance of any kind. The mechanical arrangements which have been put forward as perpetual motions by inventors are either, (1) Systems of weights, which are allowed to slide on a wheel into such positions relatively to the axis of the wheel as to produce a constant turning moment in one direction; (2) Masses of liquid moving in wheels on the same principle; (3) Masses of iron arranged on the same principle, but subjected to the attractions of magnets instead of their own weights. Numbers of patents for such machines were frequently taken out, but in every case the inventors showed an ignorance of the most elementary principles of physics.
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PERSISTENCE

In physics, persistence is the continuance of an effect after the cause which first gave rise to it is removed; as, the persistence of the impression of light on the retina after the luminous object is withdrawn; the persistence of the motion of an object after moving force is withdrawn.
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PERSPEX

Perspex is a trade name for polymethyl methacrylate.
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PERSULPHATE

A persulphate is a salt of persulphuric acid. The persulphates have strong oxidizing characteristics useful in industry. Ammonium persulphate was formerly used for reducing the density of photographic negatives.
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PERSULPHURIC ACID

Persulphuric acid is obtained from electrolyzing sulphuric acid, and is used for producing persulphates.
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PERTURBATIONS

Perturbations are the orbital irregularities or deviations of the planets from their regular elliptic orbits. These deviations arise, in the case of the primary planets, from the mutual gravitations of these planets towards each other, which derange their elliptic motions round the sun; and in that of the secondaries, partly from the mutual gravitation of the secondaries of the same system, similarly deranging their elliptic motions round their primary, and partly from the unequal attraction of the sun on them and on their primary. Of the planetary perturbations, the most important in a practical point of view are those which arise from the mutual attractions of the three bodies, the sun, the earth, and the moon.
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PETRI DISH

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A petri dish is a shallow, circular, glass or plastic dish with a loose-fitting cover which is used for cultivaying bacteria and other micro-organisms. It was named after the German bacteriologist J R Petri.
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PETRIFYING LIQUID

A petrifying liquid is a thin emulsion used instead of water in decorating, when thinning down an oil-bound water paint for exterior use or for use on a very hot surface.
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PETROL

Petrol is a volatile, flammable liquid mixture of hydrocarbons, obtained from
petroleum and used as a fuel for internal-combustion engines.
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PETROLATUM

Petrolatum is a tasteless, odourless, pharmaceutical substance consisting essentially of the refined residue resulting from the distillation of petroleum. Petrolatum is frequently known by the brand names 'Vaseline' and 'Cosmoline', and is used as a lubricant and as a balm for chapped skin.
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PETROLEUM

Petroleum is an oily, thick, flammable, usually dark coloured liquid that is a form of bitumen or a mixture of various hydrocarbons, occurring naturally in various parts of the world and often separated by distillation into petrol, naphtha, benzene, kerosene and paraffin.

Petroleum was known to the Indians of Western New York, and it was collected in small quantities by them and by the early settlers of New York and Pennsylvania, amounting sometimes to as much as twenty barrels in a year. The first organized and successful effort to bore for petroleum was made in 1854 by a New York company along Oil Creek, New York. Oil was struck at seventy-one feet, and as much as a thousand barrels per day was obtained. Oil fields were quickly located elsewhere in New York and in Pennsylvania, Ohio and West Virginia, those of Pennsylvania proving the richest. The latter yielded 3,000,000 barrels in 1862. Gasolene, naphtha, kerosene, paraffine and other products soon began to be manufactured in the USA from the petroleum.
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PETROLEUM REFINING

Petroleum refining is the processes used to produce fuels, chemicals, and gas by treatment of petroleum. Petroleum has been known and used for thousands of years, but systematic separation of its components has only been carried out for just over a century. Initially, petroleum was refined almost entirely to produce fuels. Since the Second World War the use of refinery products as a source of petrochemicals has become more important, but over 90 percent of crude petroleum is still used for fuel. The key to petroleum refining is the initial separation of hydrocarbons into various groups of similar compounds. The groups are distinguished by their boiling-points, and they are separated by fractional distillation. A group of hydrocarbons with similar boiling-points is called a fraction. Each fraction has a distinct treatment within the refinery. Fractions for which there is little demand may be converted to other fractions by later refinery processes. Refinery gas is the petroleum fraction with the lowest boiling-point, and does not condense in a fractional distillation column.

Propane and butane may be extracted from refinery gas to make liquefied petroleum gas. The residual gas, containing mainly hydrogen, methane, and ethane, is used as a fuel to operate the refinery. The most economically important product of petroleum refining is the range of fractions called petrol, which boils at 30-140 degrees Celsius. Light petrol condenses at boiling-points of 30-80 degrees Celsius, right at the top of the fractionation column. It is used to make fuel for motor cars and other petrol-engined vehicles. Next down the column, at boiling- points of 80-190 degrees Celsius, naphthas are drawn off. They may be used in blending fuels. Individual naphthas are separated and used to make solvents, and as a raw material in producing many organic chemicals. Much of the naphtha fraction is reformed for use in petrol. The fraction next below the naphthas in the fractionation column condenses at boiling-points of 190-250 degrees Celsius. This fraction contains the kerosenes, which include paraffin, traditionally burnt with a wick for heating and lighting. This fraction is now more important for making aviation fuel for jet aircraft. The final group of fractions condensing in the column is diesel oil, or gas oil, with boiling-points in the range 250-350 degrees Celsius. Their main use is in diesel engines.

Heavier oil which does not evaporate in the initial fractional distillation passes through the bottom of the column. In some refineries these residues pass on to another stage of vacuum distillation. Products separated this way include lubricating oils and petroleum jelly (used as a grease, or as a base for making ointments). Separating individual compounds from the various fractions and residues is done by several methods. Solvent extraction, for example, is another way of extracting lubricating oil from residues. Further solvent treatment can eliminate undesirable contaminants from lubricating oil or kerosenes. Some substances are removed or separated by crystallization, in which the heavier fractions are cooled until waxes crystallize, and other semi-solids solidify. The solid particles are then filtered out. Preparing fractions or products for final use involves many complicated processes. Impurities, of which the most important are sulphur compounds, are generally removed by hydro treatment.

In blending, different fractions are mixed to achieve specific properties. For example, fuel-oils for domestic and industrial heating are a blend of heavy residue oils with lighter fractions which reduce their viscosity. Oils to be burnt in engines generally need fuel additives blended in to improve their performance and safety. Chemical treatment of fractions to change them into other fractions or into feedstocks for petrochemicals is a large and growing part of refinery work. These processes include cracking, in which heavier hydrocarbons in residues are broken down into lighter fractions, particularly petrol. In hydro treatment, unsaturated hydrocarbons may be saturated with hydrogen. To make slightly heavier hydrocarbons, or to turn straight-chain molecules into ring molecules, a reforming process is used. This produces more petrol, and many aromatic hydrocarbons for use in the chemical industry to make explosives, synthetic rubbers, food preservatives, and many other specialist chemicals.

Other building-up processes include polymerisation, in which identical molecules combine, and alkylation, in which hydrocarbon groups or chains are added to molecules. Storage facilities are a vital part of the work of a refinery, which may have hundreds of tanks, generally above ground and about 30 metres in diameter. A huge network of pipes connects the tanks with various processes, so that a tank may be used for storing intermediate fractions, separate compounds, or finished product awaiting transport to users or chemical factories. Large tanks hold the crude oil delivered to the refinery, with each tank used for oil from a particular source. Switching between crude tanks enables selection of the crude to give the properties best suited to the refinery's current workload. Transport of crude to the refinery is by pipeline or by oil tanker (most refineries are near the sea). Transport of finished products is generally by pipeline, road, or rail.
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PEWTER

Pewter is an alloy of tin and lead, or of tin with proportions of lead, zinc, bismuth, antimony, or copper, and used for domestic utensils. One of the finest sorts of pewter is composed of 100 parts of tin to 17 parts of antimony, while the common pewter of which beer-mugs and other vessels were made consists of 4 parts of tin and 1 of lead. The kind of pewter of which tea-pots were made (called Britannia-metal) is an alloy of tin, brass, antimony, and bismuth.
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PFS:FIRST CHOICE

PFS:First Choice by Software Publishing Corporation, is a software package that integrates the power and ease of use of the original pfs: products into one menu-driven product. This product combines spreadsheet, word processing, data management, reporting, communications, and graphics functions into a compact program designed for the beginning or occasional computer user. The First Choice spreadsheet is more intuitive than the spreadsheets in other integrated packages. All entries are typed directly into the cell where they will appear instead of being entered on a command line and then inserted. The Quick Entry key allows automatic entry of a series of related headings such as months of the year. Begin by typing January and then use the Tab key to enter February, March, and April. The First Choice word processor offers a conversion utility that allows quick conversion of files from other popular word processing programs such as Microsoft Word and WordPerfect. Documents created in the word processing module can be viewed or printed as a slide using
custom fonts and styles. You can create on-screen presentations combining both text and graphic charts.
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PGP

Pretty Good Privacy (PGP), from Phil's Pretty Good Software, is a high security cryptographic software application for MS-DOS, Unix, VAX/VMS, and other computers. It uses public-key encryption to protect E-mail and data files. Allowing users to communicate securely with people they have never met, with no secure channels are needed for prior exchange of keys. PGP is well featured and fast, with sophisticated key management, digital signatures, data compression, and good ergonomic design.
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PH

pH (potential of hydrogen) is a measurement of acidity or alkalinity in terms of hydrogen ion content. Pure water has a pH of seven, or neutral. Acids have a pH less than seven, and alkalis a pH greater than seven.
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PHASE

In audio engineering phase is the frequency coherence of a signal. If two signals are out of phase, the trough of the first waveform corresponds with the peak of the second, resulting in cancellation.
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PHASE MODULATION

Phase modulation is a radio modulation technique similar to FM, that varies the carrier frequency of a transmitter in accordance with the strength and frequency of the modulating signal.
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PHENOL FORMALDEHYDE RESINS

Phenol formaldehyde resins (phenol resins or PF resins) are materials produced by the interaction of phenol and formaldehyde under a variety of conditions and were the first synthetic resins made on a large scale.
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PHENOLPHTHALEIN

Phenolphthalein is a derivative of triphenyl-methane, formed when phthalic acid is heated with phenol in the presence of a dehydrating agent. It is a pale yellow solid that is soluble in alcohol, and forms bright red compounds with alkalis, that are decomposed by the weaker acids - even carbon dioxide. On account of this it is used as an indicator in acidimetry.
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PHENYL BENZENE

Phenyl benzene is a colourless crystalline organic compound. It can be made by passing benzene through a red-hot tube, when condensation takes place with the formation of
phenyl benzene. It also occurs in coal-tar, and it is used in organic syntheses.
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PHILIPS D2999

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The Philips D2999 was a General coverage portable communications receiver manufactured between 1986 and 1989 and providing coverage from 150 khz to 30 Mhz in AM and SSB modes plus the VHF broadcast band in FM mode. The D2999 was aimed more at the domestic market than the amateur radio enthusiast, and as such made up for what it lacked in performance in audio quality.
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PHILOLOGY

Philology is the branch of knowledge that deals with the structure, historical development, and relationships of a language or languages. Some one who studies philology or is an authority on philology is known as a philologist.
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PHLOGISTON

Phlogiston was a name applied, before the time of Lavoisier, to a hypothetical substance supposed to be contained in all combustible bodies.
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PHON

The phon is the unit of loudness.
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PHONETICS

Phonetics is the science of the various sounds pertaining to human speech, their distinctive characteristics, the voice-mechanism by which they are uttered, and the methods by which they may be best represented to the eye. Any system of writing is strictly phonetic when by it each different sound is represented by a different character, and the same sound always by the same character.
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PHONO PLUG

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A phono plug is a type of coaxial push-on connector, especially used in audio equipment.
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PHONOCINEMATOGRAPH

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The phonocinematograph or kinetophone or biophotophone, was an early device for presenting moving pictures with a synchronised sound track.
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PHONOGRAPH

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The phonograph was a device invented by Thomas Edison in 1877 for recording and reproducing sounds upon tin foil. The original phonograph consisted of a grooved cylinder about three inches in diameter, covered with tin foil. The cylinder was revolved and slowly moved endways by means of turning a handle. On each side of the cylinder was a recorder with a diaphragm and steel needle which indented the foil in response to the sound vibrations received through a tube attached to a mouth-piece. The concussion of the sound-waves striking upon the diaphragm forced the metal point forward, which was already in contact with the tin-foil, and made indentations as the cylinder revolved with the movement of the crank. Several hundred of these machines were put upon the market, and quite a number were sold; but the phonograph failed to make a success.

Believing in the possibility of making a successful machine to record and reproduce sounds, Professor Alexander Graham Bell, Dr. Chichester A Bell, and Sumner Tainter associated themselves together, and after several years effort invented the graphophone. The word graphophone is a simple transposition of the word phonograph, and was intended to convey the same meaning. Tainter soon saw that tin-foil presented a surface unfit for the purpose it was called upon to fulfil, because of its pliability and destructibility. Many and elaborate experiments were made-to discover a substance upon which a perfect and durable sound record could be made. It was finally decided to use a paper surface coated with a preparation composed of wax and paraffin. The graphophone of 1892 was made in two forms, one to make the records upon a cylindrical surface, the other upon a disk or flat surface; the same principles, however, governing each machine. The machines were provided with two diaphragms, one used in making the record and the other in reproducing the sound. The cylindrical machine stood about 5 or 6 inches high by 8 inches wide, and weighed about 10 lbs. There was no skill required in the manipulation of the machine, the rotation of the cylinder being accomplished by a crank or automatic motion. Upon a diaphragm 3 inches in diameter a steel point was attached, which cut a minute hair-line in the surface of the waxed cylinder upon the agitation of the diaphragm by a sound. The indentation was so slight as to be scarcely perceptible, and yet these records could be done over time and again, and were just as perfect after a hundred repetitions as they were at first. The disk machine had some advantages over the cylindrical machine, because of the fact that the record was made upon a flat surface, and appeared in the form of a spiral line. It was accurately predicted at the time that for the purpose of copying records, and possibly for preservation, the flat surface is superior -
indeed the basic design was still in use over 100 years later in the production of gramophone records. At the end of the 19th century both of these machines were able to do the amanuensis work usually done by stenographers. For instance, any one could sit before the graphophone and in ordinary tones speak into the machine. The recording could then be written by a copyist who could write from the dictation of the machine. By a neat mechanical contrivance the operator was enabled to take as many words at a time as he could conveniently remember, and should he forget any part of the sentence, by a slight pressure of the finger on a rod running along the base of the machine the reproducer would repeat the sentence.

A slightly later model of the phonograph, in use at the start of the 20th century consisted essentially of a curved tube, one end of which was fitted with a mouthpiece, while the other end (about 2 inches in diameter) was closed in with a disc or diaphragm consisting of a thin glass plate. Connected with the centre of this diaphragm was a marker, with a very small sapphire for its head, which, when the sounds were projected on the disc from the mouthpiece, vibrated backwards and forwards. This part of the apparatus was adjusted to a wax-coated cylinder which rotated on a horizontal axis. The marker consisted of a lever, weighted so as to keep it in contact with the surface of the cylinder, and according as the pressure of sound was increased or decreased, when a record was being taken; its point was inclined downwards or upwards, and thus cut more or less deeply into the wax. For the purpose of taking a record the cylinder was rotated rapidly at a uniform speed by a powerful triple-spring motor, and when sounds were received on the diaphragm a series of small indentations were made on the wax by the vibratory movement of the sapphire point, these markings having all an individual character of their own, due to the various sounds addressed to the mouthpiece.

The sounds thus registered were reproduced by approaching the diaphragm and marker towards the wax as at first commencing, at the point where it was when the cylinder originally started, and then once more setting the cylinder in motion. The indentations previously made then caused the point to rise or fall or otherwise move as the markings passed under it, and the result was that the diaphragm was thrown into a state of vibration exactly corresponding to the movements induced by the markings, and thus affected the air around so as to produce sounds; while these vibrations, being exactly similar to those originally made by the voice or otherwise, necessarily reproduced these sounds to the ear. In these later models the same cylinders could be used a large number of times, the previous recording being shaved off and a new surface obtained.
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PHONOMETER

A phonometer is an instrument for ascertaining the number of vibrations of a given sound in a given space of time.
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PHOSGENE

Phosgene is a colourless, fuming toxic gas formed by the union of carbon monoxide and chlorine in sunlight, or by the oxidation of chloroform by sulphuric acid and potassium bichromate. It is decomposed by water.
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PHOSPHATE

In chemistry, phosphate is the generic term for the salts formed by the union of phosphoric anhydride with bases or water or both. They play a leading part in the chemistry of animal and plant life, the most important in this connection being the phosphate of soda, phosphate of lime, and the basic phosphate of magnesia. In agriculture the adequate supply of phosphates to plants in the form of manures becomes a matter of necessity in all deplenished soils. These phosphatic manures consist for the most part of bones, ground bones, mineral phosphates (apatite, phosphorite, coprolites), basic slag, superphosphates and reduced superphosphates (both prepared by treating broken-up bones with vitriol), bone-ash and phosphatic guano.
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PHOSPHATING

Phosphating is the name of various processes used to increase the corrosion resistance of bright sheet steel, such as used in the motor car industry.
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PHOSPHIDES

Phosphides are compounds of phosphorus with one other element, more especially with the metals.
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PHOSPHORESCENCE

Phosphorescence is the property which certain bodies possess of becoming luminous without undergoing obvious combustion. It is sometimes a chemical, sometimes a physical action. Certain mineral substances exhibit the phenomenon when submitted to insolation, to heat, to friction, to electricity, or to cleavage. Rain, water-spouts, and meteoric dust sometimes present a self-luminous appearance. Several vegetable organisms, chiefly cryptogams, exhibit this kind of luminosity; but the most interesting cases of phosphorescence occur in the animal world, the species in which the luminous property has been observed belonging nearly to every main group of the zoological series.

In some of the lowest life forms and in many of the jelly-fishes the whole surface of the body is phosphorescent; in other organisms the phosphorescent property is localized in certain organs, as in the sea-pens, certain annelids, the glow-worms, fire-flies, etc; while many deep-sea fishes have shining bodies embedded in the skin. The phosphorescence of the sea is produced by the scintillating or phosphorescent light emitted from the bodies of certain microscopic marine animals, and is well seen on the surface of the ocean at night.
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PHOSPHORIC ACID

Phosphoric acid can exist as a crystal or clear liquid. It is an oily, thick, colourless, and odourless liquid, or a thick, colourless, unstable crystalline solid. It is used in the manufacture of phosphates, such as salts, soaps, and detergents; fertilizers; yeasts; fire control agents; opal glass; electric lights; dental cements; waxes and polishes; gelatin; ethylbenzene, propylene, and cumene; and soft drinks. It is used as an acid catalyst, soil stabilizer, antioxidant in food, acidulant and flavour agent in jellies and preserves, bonding agent for refractory bricks, and petrol additive. It is also used in the rust proofing and polishing of metals, cotton dyeing, tile cleaning, extracting penicillin, hot stripping for aluminium and zinc substrates, ceramic binding, water treatment, process engraving, electro-polishing, coagulating of rubber latex, operating lithography and photoengraving operations, and pickling. It is used to manufacture the phosphoric acid electrolyte fuel cell system which has created the largest fuel cell built and has been used to treat lead poisoning.

Phosphoric acid is incompatible with strong caustics and most metals. It readily reacts with metals to form flammable hydrogen gas. The liquid can solidify at temperatures below 21 degrees C. It is corrosive to ferrous metals and alloys. It is soluble in alcohol and hot water. It can form three series of salts: primary phosphates, dibasic phosphates, and tribasic phosphates. It is deliquescent and hygroscopic. It is a chelating agent. It has a low vapour pressure at room temperature. Phosphoric acid is also known as orthophosphoric acid, metaphosphoric acid, and white phosphoric acid.
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PHOSPHOROSCOPE

A phosphoroscope is an instrument designed to show the phosphorescence of certain bodies that emit light but for a very short period. By its means many substances previously unsuspected of phosphorescence were proved capable of retaining light for very short periods. The name is also given to a philosophical toy for showing phosphorescent substances in the dark.
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PHOSPHORUS

Phosphorus is a non-metallic element of the nitrogen family that occurs widely as a phosphate. It has the symbol P.

Phosphorus is an essential ingredient of all living things, and is present in well-marked amounts in nervous tissue and bones, composing in combination, as calcium phosphate, about 17 percent of the ash of bone. Ordinary phosphorus is a waxy solid that is colourless when pure, and forms brilliant, highly refractive crystals when sublimed in a vacuum, though usually it is more or less coloured pale yellow or buff from the action of light or the presence of impurities. It is practically insoluble in water, but dissolves freely in carbon disulphide and sulphur chloride, being also soluble, though to a lesser extent, in chloroform, aniline, and oils.

Phosphorus is most marked chemically by the readiness with which it is oxidized: thus, it glows and gives off fumes of a garlic odour when exposed to the air, and this reactions often generate enough heat to ignite the sample. When ignited in the open air phosphorus burns with a dazzling white light, forming a snowy deposit of phosphoric anhydride.
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PHOSPHORUS ACID

Phosphorus acid is a powerful reducing agent. It is formed by acting on phosphorus trichloride with water or hydrochloric acid, and cab be obtained crystalline by evaporating the solution. It behaves as a dibasic avid, and is decomposed on heating, giving off spontaneously inflammable phosphine and forming metaphosphoric acid.
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PHOT

A phot is a unit of luminous flux equal to the illumination produced by one lumen on a surface of one square centimetre.
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PHOTO-ENGRAVING

Photo-engraving is engraving by photography, a name for processes in which the action of light on a sensitised surface is made to afford a printing surface corresponding to the original from which the photographic image was derived.
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PHOTO-HELIOGRAPH

The photo-heliograph was an instrument used for observing the transits of Venus and other solar phenomena, consisting of a telescope mounted for photography on an equatorial stand and moved by suitable clockwork.
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PHOTOGRAPHY

Photography (from the Greek Photos meaning light and grapho meaning I write) is the art of taking representations of objects by the action of light through the lenses of a camera on a previously prepared surface or electronic sensor.

Early cameras operated upon the principle of allowing light reflected from a subject to fall upon a light-sensitive chemical impregnated plate, later plastic film. These plates or films were then treated with other chemicals to prevent further sensitivity to light, thereby fixing the image which was then printed. Later digital cameras evolved which used electronic light sensors to record the image in a binary digital file on a memory card.

If too much light is allowed in to the camera, the picture will be over exposed, and will look bright and indistinct. If not enough light is allowed in, the picture will be under exposed and will look dark and indistinct. It is less common for photographs to be over exposed, than under exposed.

Light is allowed in to the camera to the photograph plate, film or sensor through a quickly opening and closing door called the shutter. The size of the hole which is revealed by the shutter is known as the aperture, and is measured in F-Stops, such as F1.8, F4.5, F11 etc. Where, confusingly, the larger the F number the smaller the aperture is. Thus, F1.8 is quite a large aperture, and F11 is fairly small. A larger aperture, represented by a smaller F number, lets in more light than a smaller aperture.

The length of time for which the shutter remains open, letting light in through the aperture is often referred to as the shutter speed, and is measured in fractions of a second. Thus, a shutter speed of 500 implies that the aperture will be open for 1/500th of a second, while a shutter speed of 125 implies that the aperture will be open for 1/125th of a second. The longer the aperture remains open, the more light will enter.

How quickly the photographic plate, film or sensor reacts to the light reaching it through the aperture is known as the sensitivity of the plate, film or sensor and is measured in ISO or ASA units. The larger the ISO value, the quicker the plate, film or sensor will react to the light. Thus, a sensitivity of ASA or ISO 100 will react slower than a sensitivity of 200 or 400.

The aperture size, shutter speed and sensitivity, work together to determine the level of exposure that occurs when a picture is taken. Automatic camera settings will set these three values for you, so that the picture is properly exposed, and if it can not be properly exposed, will warn you. However, there are other effects connected with each of these three settings.

The higher the sensitivity of the photographic plate, film or sensor, the more grainy or noisy the photograph will be. Therefore, using the lowest possible sensitivity will give the best possible quality for the photograph. In order to use a low sensitivity, the subject must be as brightly lit as possible. For example a subject in bright sunshine or lit by powerful lamps or the use of a camera flash gun.

The camera's aperture size governs the depth of the photograph. The smaller the aperture is, the deeper the field of focus. Using a large aperture size will result in only the subject being in focus, objects behind and in front of the subject will be blurred. Using a small aperture will allow objects behind and in front of the subject to also be in focus. The smaller the aperture size, the further behind and in front of the subject objects will remain in focus, and by extension the easier it will be to focus upon the subject.

The most noticeable effect of the shutter speed is in reducing motion blur and camera shake. When holding a camera, particularly one with a long lens every one will quiver their hand to a greater or lesser degree. When using a zoom lens, this quivering or camera shake is much more noticeable than when using a shorter or wider angle lens. If the camera is moved, even slightly while the shutter is open, the picture will be blurred. The more the camera moves while the shutter is open, the more blurring will occur. By using a fast shutter speed, the shutter is open for less time and as such less movement affect the photograph. Similarly, if the subject being photographed moves while the image is being taken, the resulting photograph will be blurred. Using a fast shutter speed of 1/500th of a second or faster enables photographs to be taken of action shots, such as footballers in mid-movement or in the air while heading the ball. The subject's movement being slower than the speed of the shutter opening and closing which appears to freeze the moment in time.

The best way to reduce camera shake is to use a tripod. If you can not use a tripod, try resting the camera on a firm surface, such as a wall, fence post or tree. It can not be over emphasised that using a tripod will result in better photographs as every one quivers ever so slightly when taking photographs. Even activating the shutter release on the camera can slightly jar the camera. To overcome this, many photographers use a camera with automatic frame advance or sequential shooting, whereby after activating the shutter release the camera takes multiple photographs until the shutter release mechanism is released. In this way, three images may be taken automatically, the first and last will often suffer from slight camera shake due to the action of operating the shutter release mechanism, while the second image will not.

Photography originated in the 19th century, as early as the commencement of the nineteenth century, Thomas Wedgwood (son of the potter) had discovered a method of copying paintings on glass and of making profiles by the action of light upon silver nitrate; but these pictures were not permanent. About 1814 Nicephore Niepce in France discovered a method of producing, by means of the camera obscura, pictures on plates of metal coated with asphaltum, and at the same time of rendering them permanent. In 1839 Daguerre announced the discovery of the Daguerreotype. In the meantime, however,. Henry Fox Talbot had discovered the process of obtaining pictures in the camera by the agency of light on paper coated with silver chloride silver nitrate, and also of fixing them when so obtained. Talbot gave the name of calotype to his process (also called talbotype).


Numerous modifications of the calotype were introduced, besides various new photographic processes, the most important of the early being those of Niepce de St Victor and Scott Archer, the former of whom introduced the use of albumen and the latter that of collodion as a substitute for paper, these substances being in either case thinly spread over a plate of glass. Archer perfected the wet collodion process, and published full working details in 1851. Collodion dry plates were introduced by Hill Norris in 1856; collodion emulsion dry plates by Messrs. Sayce and Bolton in 1864. In 1871 Dr. R L Maddox discovered that glass plates could be coated with an emulsion consisting of silver bromide contained in gelatine. This gelatine dry-plate process was improved by Bennett in 1878, and came into general use about 1880. For many years it was almost the only process employed in ordinary photography; but instead of glass a thin transparent film of celluloid was very commonly used.

Photographs may be either negative or positive. Negative photographs are produced in the camera, and exhibit the lights and shades contrary to nature, that is, the lights dark and shades white. Gelatino-bromide dry plates were 'developed', after the image was taken, in a dark room (with a subdued red light for working by), the developer in common use being a solution of pyrogallic acid, potassium bromide, and an alkaline carbonate, in suitable proportions; there were, however, other solutions that could be used. The plate was then washed, and fixed in a solution of sodium hyposulphite, washed again, and then dried.

Daylight developers were invented around 1900, the developing being effected in a closed box by a kind of mechanical process. In order to obtain prints or positives, showing-lights and shadows in natural relation, several methods were used. In silver printing a paper sensitized by being floated on a solution of albumen mixed with common salt, and then on a solution of silver nitrate was placed in close contact with the negative in a printing-frame, and exposed to light until the silver compounds had become sufficiently darkened. The picture was afterwards toned, fixed, and washed. A common toning medium was a neutral or slightly alkaline solution of gold chloride, the print being afterwards fixed with hyposulphite. In the platinotype process the paper was sensitized by ferric oxalate and a double salt of potassium and platinum. After exposure under a negative it was developed by floating on a hot solution of neutral potassium oxalate, when the picture appeared in rich platinum black. It was fixed in weak acid and washed in water. Another printing paper formerly largely used was 'bromide' paper, invented by Swan of Newcastle. It was gelatino-bromide of silver emulsion coated on paper, and was developed and fixed in a similar manner to dry-plates.

In 1855 Poitevin devised a process by which pictures of great beauty and permanence were obtained. He combined carbon or some other pigment, in a fine state of division, with gelatine, starch, or gum, applied it over the surface of his paper, dried it, submitted it to the action of light under a photographic negative, and so first produced what was usually called a carbon print. In 1864; carbon-printing was brought to a high state of perfection by Dr. Swan, whose plan was to prepare a solution of gelatine and bichromate of potash (the latter being the sensitizing agent), mixed with some black pigment, and apply the mixture as a coating to a sheet of paper, and print his positives on the black cake, or tissue as it was called, thus produced. One of the most important discoveries in connection with photographic printing was that of Walter Woodbury. By his process the hardened tissue was brought into contact with a plate of type metal under considerable pressure. The plate took the impression of the relief, and pictures were printed from it instead of from the raised tissue. The autotype process, invented by Johnson, was a more simple and ready method of carbon-printing than the carbon process proper, but the principles involved were the same. It was used for book illustrations and picture reproduction.

Photo-lithography, the process of reproducing copies of a photograph from a lithographic stone, was discovered byAsser of Amsterdam in 1859. Various modes of multiplying photographic pictures by photolithography have been successfully tried. A common mode was to take a print on paper sensitized with gelatine and bichromate of potassium, and to ink it with a suitable oily ink. This ink adhered to the parts where the gelatine had been acted on by light and had become insoluble, but where the gelatine was still soluble the ink could be easily washed off. It was then transferred to a lithographic stone in the usual way.

In photo-zincography the process consisted in projecting an impression on a plate of prepared zinc by photography and then engraving it by etching with acids, so that copies could be printed from the plate.

Relievo surface-printing blocks, commonly known as 'half-tone blocks', reproduced the shades of a photograph by splitting up the blacks into lines or dots of various sizes. This was effected by the use of a screen or grating of opaque crossed lines, 100 to 200 to the inch, ruled on glass. The drawing or photograph to be reproduced was photographed on a wet collodion plate, which had a lined screen placed parallel to and within 1/8th of an inch of it. A negative was thus obtained consisting of opaque black dots varying in size in inverse ratio to the lights and shades of the original, and was then made ready for printing on metal. A copper plate, coated with a solution of albumen, gelatine, or glue, was sensitized and exposed under the negative, thus receiving the picture. The plate was etched, and was subsequently mounted so as to be 'type-high', and could be printed along with ordinary type.

After the introduction of the gelatine plate the art of photography made immense advances, and its applications were quickly recognised as being endless. In addition to glass plates, gelatino-bromide films coated on celluloid and forming rolls were commonly used after about 1900, one great advantage of them being that a roll, capable of receiving a number of pictures, could be carried in the camera and used by turning a handle. Hand cameras in all shapes and sizes were introduced by 1905. Instantaneous shutters were common in cameras as early as 1905, and these were so carefully adjusted by mechanical appliances that they could be regulated to a small fraction of a second, or a prolonged exposure could be given to the subject at will. These instantaneous processes enabled scientists to analyse muscular movements and the various modes of locomotion (running, flying, etc.). The cinematograph (what we now call films or movies) depended for its existence upon the taking of instantaneous photographs.

Cameras for taking panoramic views, embracing nearly a semicircle, date back to the daguerreotype days and by 1905 there were several excellent panoramic cameras in use. Lenses were much improved since the introduction of 'Jena' glass in 1885; the 'anastigmats' made with this glass have a greater rapidity than older forms, extreme fineness of definition over an extended area of illumination, and freedom from astigmatism, and they were very compact. A later invention was the 'fluid lens' of Dr. Grun, in which a fluid of high refractive power was inclosed between the lens combinations. With this lens it was possible to take photographs in theatres solely by the ordinary light of the footlights and limelight, with an exposure of less than a second; photographs of landscapes could be taken on moonless nights in thirty seconds. With the tele-photo lens of Dallmeyer one could obtain enlarged images of distant objects; it consisted of a tube with an ordinary photographic doublet in front and an achromatic negative lens system behind.

At the start of the 20th century remarkable results were attained in the application of photography to astronomy, and heavenly bodies not otherwise observed were thus detected. The photographing of objects as magnified by the microscope (microphotoyraphy) was another development. The application of photography in book-illustration was very successful, and largely took the place of wood-engraving by 1900. Photography by means of artificial light (electric light, flashlight) was also regularly practised as early as 1905.

Colour photography was a later development in photographic science. None of its earlier investigators met with any practical success. The nearest approach to the solution of the problem wa ue to Frederick E. Ives of Philadelphia, who, by the application of a new and definite principle of colour selection in 1888, and by the subsequent invention of adequate devices for carrying out the process in a simple manner, realised a practical means for reproducing the colours of nature by photography. Ives devised a camera by means of which the rays of light, after passing through the lens, were split up into three sets, one set being filtered through red glass, another through green, and another through violet, producing three separate negatives on different parts of a dry-plate. These three negative images represented the effect of the three fundamental colour sensations, and a triple positive on glass, made therefrom by contact printing on another dry-plate, was placed in an instrument called by Ives a 'Kromskop', into which one looked and saw a true representation of the object photographed, in all its beauty and subtlety of colouring.

Modifications of Ives's process were devised by Dr. Joly of Dublin, and Professor Wood of Wisconsin University, the former using glass screens ruled with transparent inks of red, green, and violet, and the latter using diffraction gratings. A very important development of this three-colour process was the application of photo-mechanical methods to the production of prints in colour. Ives's process was followed up to the point of the production of the three positives representing the three-colour sensations, and half-tone blocks were made from these. The three primary pigments or printing inks were the complementaries of the three primary colour sensations, so that the block produced from a negative taken through red glass had to be printed in cyan-blue ink, that taken through green glass in magenta-pink, and that taken through violet glass in pale primrose-yellow. By three prints superimposed from three blocks, yellow, red, and blue in succession, a reproduction of a picture in its natural colours was obtained.

In 1914 the first still camera using 35 mm motion-picture film was produced, but it wasn't until after the introduction of the Leica camera in 1924 that miniature photography (the familiar domestic photography of modern times) became popular. The original Leica camera was developed by Barnack for testing motion-picture film. In the 1950's sub-miniature cameras were invented using film smaller than the familiar 35 mm. In 1963 Kodak invented the Instamatic, a camera which took a special cassete that didn't require any special threading of the film. By 2010 film cameras have all but been replaced by digital cameras, the film being replaced by an electronic sensor and the images stored in a digital format on a memory card, either internal to the camera or plugged in, developing taking place within the camera or externally on a computer, but in both cases electronically without the use of special papers, chemicals and the need for a special darkroom.
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PHOTOGRAVURE

Photogravure is a process of engraving in which by the aid of photography subjects are reproduced as plates suited for printing in a copper-plate press. The process known as heliogravure is essentially the same.
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PHOTOMETER

A photometer is an instrument intended to indicate relative quantities of light, as in a cloudy or bright day, or to enable two light-giving bodies to be compared. Photometers depend on one or other of the two principles, that the eye can distinguish whether two adjacent surfaces are equally illuminated, and whether two contiguous shadows have the same depth. Bunsen's photometer is based on the former principle, Rumford's on the latter. The common unit for comparison was the light emitted by a sperm-candle burning 120 grainy of spermaceti per hour, other lights being said to have the intensity of so many candles. Improved forms of photometers for more easily obtaining the illuminating power produced by coal-gas and the electric light were later introduced.
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PHOTOMETRY

In physics, photometry is the measurement of the luminous intensity of a light source, or the amount of luminous flux falling upon a surface from such a source. Photometry is important in photography , astronomy, and illumination engineering. Instruments used for photometry are called photometers. Light waves stimulate the human eye in different degrees, depending on the wavelength of the light. Because it is difficult to make an instrument with the same sensitivity for different wavelengths as the human eye, many photometers use a human observer. Photoelectric photometers need special collared filters to make them respond like the human eye. Instruments that measure radiant energy instead of light are called radiometers, and must be made equally sensitive to all wavelengths. The intensity of a light source is measured in candle power, usually by comparing the source with a standard source provided by the National Bureau of Standards. The known and unknown sources illuminate portions of a window surface side by side, and their distances are adjusted until the illumination on the surface is the same. The relative intensity is then calculated from the inverse square law.
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PHOTON

In optics, a proton or troland (named after the American physicist and psychologist who introduced the unit in 1917) is a unit of retinal illumination. One photon being the illumination produced by a surface with a luminance of one candela per square metre when the pupil has an area of one square millimetre.

A photon is a light quantum, that is a discrete but definite amount of radiation proportional in magnitude to the frequency of the radiation it represents, having a frequency within the visible spectrum. A photon is emitted from an excited atom when one of the orbital electrons, having been transferred to an orbit of higher energy level, suddenly returns to its former orbit.
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PHOTOPHONE

The photophone was an instrument invented by Graham Bell and Sumner Tainter, by which sounds, including speech, could be transmitted to a distance by the agency of light. A powerful beam of light was made to fall on a very thin glass mirror, which formed a diaphragm in a bell-shaped receiver. The light was reflected from the mirror through a lens, by which the rays were rendered parallel, and then passed to the distant station. At this point the beam was received in a parabolic mirror and concentrated on a cell composed of alternate layers of brass and selenium, which was placed in series with a battery and telephone reveiver, and which had the property of diminishing in resistance when light fell on it (it was photosensitive). Sound waves were modulated with the light by coming into contact with the mirror causing it to distort and the light rays transmitted also accordingly.
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PHOTOSHOP

Adobe Photoshop is a high-end image editor originally for the Macintosh computer, but later ported to the PC under the Windows operating system. The primary strength of Photoshop comes from it's layers which enable elements of an image to be manipulated independantly of the others, a feature which was quickly copied by other lower cost image editors.
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PHOTOTROPIC

Something which is phototropic seeks light. The term is used in Biology to describe animalcules which seek the light.
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PHTHALIC ACID

Phthalic Acid is obtained by the oxidation of napthalene by means of fuming sulphuric acid and mercury. It forms colourless crystals that are soluble in water. When heated it yields an anhydride and is the parent substance of the phthalein dye-stuffs.
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PHYCOLOGY

Phycology is that department of botany which deals with the study of the algae or sea-weeds.
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PHYSICAL CHANGE

In chemistry, physical change is a change in the condition or state of a substance; it's composition is not altered.
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PHYSICAL GEOGRAPHY

Physical Geography is that branch of geography which deals with the surface of the earth, or of any part of it as regards its natural features and conformation, the changes that are constantly taking place and that have formerly taken place so as to produce the features now existing; it points out the natural divisions of the earth into land and water, continents, islands, rivers, seas, oceans, etc; treating with the external configuration of mountains, valleys, coasts, etc; and of the relation and peculiarities of different portions of the water area, including currents, wave-action, depth of the sea, salt and fresh water lakes, the drainage of countries, etc. The atmosphere in its larger features is also considered, including the questions of climate, winds, storms, rainfall, and meteorology generally. Lastly it takes up various questions connected with the organic life of the globe, more especially the distribution of animals and plants, and their relation to their environment; tracing the influence of climate, soil, natural barriers or channels of communication, etc, upon the growth and spread of plants and animals, including in the latter the various races of man. The field of physical geography is thus by no means easy to confine within strict limits, as it is so closely connected at various points with geology, mineralogy, botany and zoology, chemistry, ethnology, etc.
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PHYSICS

Physics (from the Greek, physis, nature), also formerly known as natural philosophy, is the study of the phenomena of the material world, or of the laws and properties of matter; more restrictedly it deals with the properties of bodies as bodies, and of the phenomena produced by the action of the various forces on matter in the mass. It thus has as its chief branches the subjects dynamics, hydrostatics, heat, light, sound, electricity, and magnetism.
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PHYSIOGNOMY

Physiognomy is the judging of nature and character of animals and people from external appearances. It is an ancient art, which was remodelled along broadly scientific lines by Charles Dawrwin in his book 'Expression of Emotions in Man and Animals' published in 1873. Formerly, criminology, pathology and anthropology all made extensive reliance on physiognomy, but in the later part of the 20th century it was widely discredited as a science.
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PHYSIOLOGY

In medical and biological sciences, physiology is the department of inquiry which investigates the functions of living beings. In its wide sense the living functions of both animals and plants fall to be investigated by physiology, this division of the subject being comprehended under the terms comparative physiology/ and animal and vegetable physiology. When more specially applied to the investigation of the functions in man the appellation human physiology is applied to the science. The importance of physiological inquiry in connection with the observation of diseased conditions cannot be overrated. The knowledge of healthy functions is absolutely necessary for the perfect understanding of diseased conditions; and the science of pathology, dealing with the causes and progress of diseases may in this way be said to arise from, and to depend upon, physiological inquiry. Physiology in itself thus forms a link connecting together the various branches of natural history or biology and those sciences which are more specially included within a medical curriculum.

The history of scientific physiology may be said to begin with Aristotle who attained no mean knowledge of the subject. The Alexandrian school, flourishing about 280 BC under the Ptolemies, and represented by Erasistratus, Herophilus, and others, obtained greater opportunities for the acquirement of physiological knowledge, through the investigation of the bodies of criminals who had been executed. Erasistratus thus threw much light on the nervous system and its physiology; whilst Herophilus made important observations on the pulse, and in addition discovered the lacteal or absorbent vessels. After this there was a period of decline, but Galen, living in the 2nd century after Christ, again raised the science to a respectable position, and effected a vast advance and improvement in physiological knowledge.

The systems which succeeded Galen and his times consisted, until about 1543, of absurd speculations and theories, conducive in no respect to the advance of true knowledge. In 1543 Vesalius paved the way towards the more scientific epochs of modern times by his investigations into the anatomy and structure of the human frame. In 1619 Harvey, the 'father of modern physiology,' discovered the circulation of the blood. Since this time the history of physiology has gone hand in hand with the general history of anatomy. In the 19th century physiological research was revolutionised by the introduction and extensive use of the experimental mode of investigation; and of elaborate and delicate instruments and apparatus, such as the sphygmograph, or pulse-recorder; the ophthalmoscope; the laryngoscope; and the microscope.

The different departments of physiology may be enumerated as comprehending the investigation of the three great functions which every living being performs, namely, (1) nutrition, including all that pertains to digestion, the circulation, and respiration; (2) in nervation, comprising the functions performed by the nervous system; (3) reproduction, which ensures the continuation of the species and includes also the phenomena of development.
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PHYTOLOGY

Phytology is the science of plants. The word was formerly sometimes used for the familiar term botany.
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PICK

A pick (or pick-axe) is a tool consisting of a long shaft set at right angles in the middle of a curved iron or steel bar with a point at one end and a chisel-edge or point at the other, used for breaking up hard ground, rock, etc.
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PICK GLASS

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A pick glass is a magnifying glass comprised of a small metal folding stand, which when opened is stood upon the obejct to be inspected which is then viewed in a magnified state by looking down through the lens in the top of the pick glass. Pick glasses were originated for checking the quality of woven linen.
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PICRIC ACID

Picric acid (Carbazoilic acid) or trinitro-phenol is a lemon yellow, crystalline acid, prepared by the action of nitric and sulphuric acids on phenol. It is used for dyeing silk goods after mordanting with alum. It is also used for imparting a bitter taste to beer, and as an explosive either in the form of the free acid or in one of its salts. Most of these explode violently on percussion or on detonation, and when consolidated by fusion, it is used as a high explosive for charging shells under the name lyddite. It yields explosive salts by the substitution of metals for the hydrogen of the hydroxyl group.
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PIEZOMETER

A piezometer is an instrument for measuring the compression of water and other liquids under pressure. In Oersted's piezometer the pressure is gauged by the manometer, and the amount of compression indicated by mercury in a glass tube.
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PIG IRON

Pig iron is the form in which cast iron is made at the blast furnace, being run into moulds, called pigs.
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PIKECRETE

Pikecrete is a compound, invented by a British scientist named Pike during the Second World War, comprised of 14% sawdust or wood pulp, and 86% water mixed thoroughly and frozen. The resulting compound is not only extremely strong, but also resists melting and is less dense than water. Winston Churchill planned during the Second World War to build an aircraft carrier out of pikecrete. The resulting platform would have been solid and as such resistant to bullets and torpedoes (it couldn't be 'holed' like a traditional ship) and with its thermodynamic properties would have not melted even in tropical seas for quite a long time.
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PILLOW-BLOCK

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A pillow-block is a block or standard for supporting the end of a shaft.
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PINCHBECK

Pinchbeck (also known as bath metal, Dutch gold, Dutch metal) is an alloy of 80 percent copper and 20 percent zinc once used for making cheap watch cases where it was intended to imitate gold, and more recently as a substitute for the more expensive bronze. It was invented by a London watchmaker, named Pinchbeck, in the 18th century.
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PINE

Pine is a UNIX based email system, based on Elm but with improvements which include a built-in text editor and address book.
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PINENE

Pinene is a terpene colourless liquid which smells like turpentine and occurs in pine trees and the essential oils of eucalyptus, lemon and thyme.
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PINION

In machinery, pinion is a small wheel which plays in the teeth of a larger one, or sometimes only an arbor or spindle in the body of which are several notches forming teeth or leaves, which catch the teeth of a wheel that serves to turn it round.
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PIPERIDINE

Piperidine is a secondary amine, occurring in combination with piperic acid in pepper.
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PIPERINE

Piperine is an alkaloid occurring in pepper. It is a feeble base that crystallises in prisms, and colours sulphuric acid red.
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PIPETTE

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A pipette is a tube open at both ends, used for accurately measuring off small quantities of liquids. A pipette may be straight, or provided with a bulb, and is constricted at the mouth to a narrow orifice. In using a pipette the liquid is sucked up to a little above the mark, the top of the tube closed with the finger, of which the pressure is relaxed until the liquid falls to the mark, when the flow is stopped by increasing the pressure again. The measured quantity of liquid is then allowed to flow out into the required vessel.
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PISTON

In machinery, a piston is a movable piece, generally of a cylindrical form, so fitted as to occupy the sectional area of a tube, such as the barrel of a pump or the cylinder of a steam-engine, and capable of being driven alternately in two directions by pressure on either of its sides. One of its sides is fitted to a rod, called the piston-rod, which it either moves backwards and forwards, as in the steam-engine, where the motion given to the piston-rod is communicated to the machinery, or by which the piston is itself made to move, as in the pump. The piston is usually made to fit tightly by some kind of material used as packing, the piston-rod being also made similarly tight by material closely packed in the stuffing-box.
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PIXEL

In computing a pixel is one of the dots which comprises a display or print. Resolution is often described in terms of pixels, or as dots per inch, such as '800x600' meaning 800 pixels wide by 600 pixels deep or '72 dpi' meaning 72 dots-per-inch.
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PLANE

A plane is a joiner's tool, consisting of a smooth-soled solid block, through which passes obliquely a piece of edged steel forming a kind of chisel, used in paring or smoothing boards or wood of any kind. Planes are of various kinds, as the jack-plane (about 17 inches long), used for taking off the roughest and most prominent parts of the wood; the trying-plane, which is used after the jack-plane; the smoothing-plane (7.5 inches long) and block-plane (12 inches long), chiefly used for cleaning off finished work, and giving the utmost degree of smoothness to the surface of the wood; the compass-plane, which has its under surface convex, its use being to form a concave cylindrical surface. There is also a species of plane called a rebate-plane, being chiefly used for making rebates. The plough is a plane for sinking a channel or groove in a surface, not close to the edge of it. Moulding-planes are for forming mouldings, and must vary according to the design. Planes are also used for smoothing metal, and are wrought by machinery.
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PLANE 2

In geometry, a plane is a surface such that if any two points in it are joined by a straight line the line will lie wholly within the surface.
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PLANE TABLE

A plane table is a device used in surveying and consisting of a movable telescope resting upon a flat board mounted on a tripod. By its use a reliable plan may be prepared in the field directly upon a sheet of paper pinned to the board.
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PLANIMETER

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A planimeter is an instrument by means of which the area of a plane figure may be measured. It is employed by surveyors in finding areas on maps, etc.
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PLANING MACHINES

Planing machines are machine tools for plaining wood or metal. For the former purpose the usual form has cutters on a drum rotating on a horizontal axis over the board which is made to travel underneath. The cutter-drum may be repeated underneath and at the edges, so as to plane all sides simultaneously. In planing metals the object to be planed, fixed on a traversing table, is moved against a relatively fixed cutter, which has a narrow point and removes only a fine strip at each cut.
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PLASTER OF PARIS

Plaster of paris is a form of hemhydrate plaster derived from rock gypsum crushed and heated to a temperature of 170 degrees celsius. This process removes some 75 percent of the water in the plaster, which when mixed with water sets (hydrates) very quickly. Plaster of Paris is produced in various forms, some dry very quickly but are very weak and are used for plaster casts in medicine, other forms take longer to dry but are much harder and are suitable for making and repairing outdoor ornaments. Plaster of Paris is also used for taking casts from moulds, for example in dentistry where a cast of a person's teeth is obtained from a mould, and allows a dentist to see the structure clearly, and dentures to be made to fit without the need for the patient to be present for long periods of time.
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PLASTIC

Plastic is a group of synthetic polymers made from oils and which are capable of being moulded into shape by heat or pressure or both.
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PLATININE

Platinine is a proprietary name for platinoid, a white metal alloy of copper, zinc and nickel (and sometimes also tungsten).
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PLATINIT

Platinit is a proprietary name for platinite, an alloy of iron and nickel with traces of carbon used as a replacement for platinum in some devices due to its similar coefficient of expansion.
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PLATINOID

Platinoid (popularly known as platinine) is a white metal alloy of copper, zinc and nickel (and sometimes also tungsten). Platinoid has a high electrical resistance and is used in industry for resistances and thermocouples, and is also used in manufacturing for costume jewellery and other silver-look-alike products such as mechanical pencils.
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PLEXIGLAS

Plexiglas is a trade name for polymethyl methacrylate.
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PLIERS

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Pliers are a type of small pinchers with long jaws, used for bending and cutting metal rods or wire, and for handling small objects - though not as small as one might use tweezers for - such as the parts of a watch, small screws and the like.
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PLINK86 PLUS

Plink86 Plus by Phoenix Computer Products is an overlay linker that brings modular programming to the PC. It lets you write a program as large and complex as necessary with no need to worry about whether it will fit within available memory. Plink86 Plus's automatic overlay-module technique allows programs to be divided into any number of tree-structured overlay areas, handles diskette changes, and segments the program for add-on packages. Plink86 Plus is a two-pass linkage editor that accepts any object file conforming to the Intel or Microsoft format and outputs executable program files. The first pass is for memory-segment addressing and the second creates the output file. Plink86 Plus works with Lattice C, Microsoft FORTRAN, Microsoft C 5.0, IBM FORTRAN (77), the IBM BASIC Compiler, the Turbo C compiler, and Clipper among other compilers.
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PLOUGH

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A plough is an implement drawn by animal, steam-power or tractor, by which the surface of the soil is cut into longitudinal slices, and these successively raised up and turned over. The object of the operation is to expose a new surface to the action of the air, and to render the soil fit for receiving the seed or for other operations of agriculture.

Ploughs drawn by horses or oxen are of two chief kinds: those without wheels, commonly called swing-ploughs, and those with one or more wheels, called wheel-ploughs. The essential parts of both kinds of plough are, the beam, by which it is drawn; the stilts or handles, by which the ploughman guides it; the coulter, fixed into the beam, by which a longitudinal cut is made into the ground to separate the slice or portion to be turned over; the share, by which the bottom of the furrow-slice is cut and raised up; and finally, the mould-board, by which the furrow-slice is turned over. The wheel-plough is merely the swing-plough with a wheel or pair of wheels attached to the beam for keeping the share at a uniform distance beneath the surface. Besides these two kinds there are subsoil-ploughs, drill-ploughs, draining ploughs, etc.

Every part of a plough of the modern type is made of metal, usually iron. Double mould-board ploughs are common ploughs with a mould-board on each side, employed for making a large furrow in loose soil, for earthing-up potatoes, etc. Turn-wrest ploughs are ploughs fitted either with two mould-boards, one on each side, which can be brought into operation alternately, or with a mould-board capable of being shifted from one side to the other, so that, beginning at one side of a field, the whole surface may be turned over from that side, the furrow being always laid in the same direction. One of these ploughs with two mould-boards is so constructed as to be dragged by either end alternately, the horses and ploughmen changing their position at the end of every furrow. Such ploughs are useful in ploughing hill-sides, as the furrows can all be turned towards the hill, thus counteracting the tendency of the soil to work downwards. In the later improved style of wheel-plough there are a larger and a smaller wheel, the former to run in the furrow, the latter on the land. These have also a second or skim coulter, for use in lea ploughing, to turn over more effectually the grassy surface. What was called a going-plough was essentially a number of ploughs combined, four, six, or eight shares being fixed in one wheeled frame, and dragged by a sufficient number of horses, such ploughs being formerly used on very large farms.

Steam ploughs on various principles were introduced among farmers in the 19th century, being patented in 1855. Some were driven by one engine remaining stationary on the headland, which wound an endless rope (generally of wire) passing round pulleys attached to an apparatus called the 'anchor,' fixed at the opposite headland, and round a drum connected with the engine itself. Others were driven by two engines, one at either headland, thus superseding the 'anchor'. As steam-ploughing apparatus were usually beyond both the means and requirements of single farmers, companies were formed for hiring them out. In steam-ploughing it was common to use ploughs in which two sets of plough bodies and coulters were attached to an iron frame moving on a fulcrum, one set at either extremity, and pointing different ways. By this arrangement the plough could be used without turning, the one part of the frame being raised out of the ground when moving in one direction, and the other when moving in the opposite. It was the front part of the frame, or that farthest from the driver, which was elevated, the ploughing apparatus connected with the after part being inserted and doing the work. Generally two, three, or four sets of plough bodies and coulters were attached to either extremity, so that two three or four furrows were made at once.

The 20th century saw the introduction of the tractor drawn plough which replaced horse-drawn ploughs in Britain.
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PLOUGHFOOT

A ploughfoot was an adjustable staff that was formerly attached to the beam of a plough to enable the ploughman to determine the depth of the furrow he was making.
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PLUTONIUM

Plutonium is a radioactive metal element with the symbol Pu. It was discovered by the chemists Glenn Seaborg and Edwin McMillan in 1940. The isotopes of plutonium were first prepared and studied by Seaborg and his associates in 1941. Trace amounts of the element have since been found in uranium ores, but plutonium is prepared in relatively large quantities today in nuclear reactors. Chemically, plutonium is reactive, its properties somewhat resembling those of the rare earth elements. The silvery metal, which becomes slightly yellow through oxidation caused by exposure to air, exists in six varying crystalline forms and has four different oxidation states. The metal gives off heat because of its radioactivity ; 15 different isotopes of
plutonium, ranging in mass number from 232 to 246, are known.
Plutonium-239 has a half-life of 24,360 years, and is produced by bombarding uranium-238 with slow neutrons. This forms neptunium-239, which in turn emits a beta particle and forms plutonium-239.
Plutonium is the most economically important of the transuranium elements because plutonium-239 readily undergoes fission and can be both used and produced in quantity in nuclear reactors. It is also used in making nuclear weapons. It is an extremely hazardous poison due to its high radioactivity. Plutonium-238 has been used to power equipment on the moon by means of the heat it emits.
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PNEUMATIC DESPATCH

Pneumatic despatch is a propulsion by means of compressed air or by forming a vacuum. Pneumatic railways were investigated in the 19th century but proved abortive, but propulsion by compressed air was successfully applied to a variety of practical uses. Parcels are thus conveyed, and internal communication in warehouses, hotels, etc, is carried on by its means. The most developed application of compressed air as a motive force was in connection with the telegraph service of large cities. Pneumatic despatch proved a most useful auxiliary in securing prompt and cheap collection and distribution of telegraphic messages and was first introduced in London by Latimer Clark in 1853, improved by Varley 1858, and again by Siemens in 1863.

The vehicles charged with the messages, technically called carriers, were forced through leaden tubes connecting the various stations, and from 1.5 to 3 inches diameter, by means of air-pressure at one end, or sucked through by a partial vacuum at the other. The invention of Latimer Clark and Varley required a separate tube between each pair of stations, and admitted of only a single despatch at a time; but a system of laying tubes in circuit for the continuous transmission of despatches, by means of an uninterrupted air-current in one direction, was adopted in Berlin by Messrs. Siemens and Halske in 1863, and introduced in London in 1870.

In 1905 both systems were in use in London with modifications to suit special traffic. The tubes (some 40 miles) ran in all directions. In the central districts, where the transmission was heavy, the stations were connected by a double tube, a receiving and a despatching one, forming a complete circuit, with a column of air always passing through it, and which was moved either by pressure, or by vacuum, or both. The up and down lines could be opened through their entire length, or blocked by switch-boxes at an intermediate station. The terminal stations could send carriers to be stopped by the switch-box at an intermediate station; and the intermediate station, when it knew a through carrier to be coming for one of the termini, could, if it happened to have any messages to send to that terminus, switch out the through carrier and insert its own messages without appreciable delay. The carriers in the 3 inch tubes held about 50 messages. Pneumatic tubes were also in use in Liverpool, Manchester, Glasgow, Dublin, etc. The circuit system, but not with a continuous current, was extensively used in Paris. The tubes were of iron, two feet in diameter. Other European cities had similar systems. New York operated the English system, but brass instead of lead tubes were employed.
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PNEUMATIC POWER

Pneumatic power is power provided by the utilization of the elasticity of the air, and especially by means of compressed air. An early use of pneumatic power was when compressed air was successfully employed in 1861 in the excavation of the Mont Cenis Tunnel, percussion drills being thus driven, and the air being compressed by water-rams. Some time after, the use of compressed air furnished from a central station was begun in Paris, and now there are thousands of people in various industries who make use of compressed air distributed by many miles of pipes. In tramways and coal-mines it is employed in some localities, especially in America. Air-brakes on railways have long been in use, and pneumatic tools for different purposes became quite familiar after about 1900, America having taken the lead in the introduction of these.
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PNEUMATICS

Pneumatics is the branch of physicswhich treats of the mechanical properties of elastic fluids, and particularly of atmospheric air. The chemical properties of elastic fluids (air and gases) belong to chemistry. Pneumatics deals with the weight, pressure, equilibrium, elasticity, density, condensation, rarefaction, resistance, motion, etc, of air; it also deals with the air considered as the medium of sound (acoustics), and as the vehicle of heat, moisture, etc. It also comprehends the description of those machines which depend chiefly for their action on the pressure and elasticity of air, as the various kinds of pumps, artificial fountains, etc. The weight of the air, and its pressure on all the bodies on the earth's surface, were perhaps unknown to the ancients, and we only have evidence of their first being perceived in the middle of the 17th century by Galileo, when a sucking-pump refused to draw water above a certain height; and Torricelli, his pupil, was the first to give a natural explanation of the phenomenon.
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POINT

In geometry, a point is a quantity which has no parts, or which is indivisible, or which has position without magnitude. Points may be regarded as the ends or extremities of lines. If a point is supposed to be moved in any way, it will by its motion describe a line.
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POINTCAST NETWORK

PointCast Network is a free computer program for the IBM PC. It is the Internet news network that appears instantly on your computer screen, with headlines that run dynamically across the screen. All you have to do is click on an item for detailed information. PointCast broadcasts national and international news, stock information, industry updates, weather from around the globe, and sports scores.
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POLAR DISTANCE

Polar Distance is the angular distance of any point on a sphere from one of its poles; more especially, the angular distance of a heavenly body from the elevated pole of the heavens. It is measured by the intercepted arc of the circle passing through it and through the pole, or by the corresponding angle at the centre of the sphere. According as the north or south pole is elevated we have the north polar distance or the south polar distance.
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POLAR FORCES

In physics, polar forces are forces that are developed and act in pairs with opposite tendencies, as in magnetism, electricity, etc.
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POLARISATION OF LIGHT

The polarisation of light is an alteration produced upon light by the action of certain bodies by which it is made to change its character. A common ray of light exhibits the same properties on all sides, but any reflected or refracted ray, or a ray transmitted through certain media, exhibits different properties on different sides, and is said to be polarised.

The polarization of light may be effected in various ways, but chiefly in the following: (1) By reflection at a proper angle (the 'polarising angle') from the surfaces of transparent media, as glass, water, etc. (2) By transmission through crystals possessing the property of double refraction, as Iceland-spar. (3) By transmission through a sufficient number of transparent uncrystallized plates placed at proper angles. (4) By transmission through a number of other bodies imperfectly crystallized, as agate, mother-of-pearl, etc.

The knowledge of this singular property of light has afforded an explanation of some interesting phenomena in optics. A simple example of polarisation may be illustrated by two slices of the semi-transparent mineral tourmaline cut parallel to the axis of the crystal. If one is laid upon the other in a perpendicular position they form an opaque combination. If one is turned round upon the other at various angles it will be found that greatest transparency is produced in the position corresponding with the natural position they originally occupied in the crystal, an intermediate stage being that when they are rotated through 45 degrees to each other. The light which has passed through the one plate is polarised, and its ability to pass through the other plate is thus altered. Reflection is another very common cause of polarisation.

The plane of polarisation is that particular plane in which a ray of polarised light incident at the polarising angle is most copiously reflected. When the polarization is produced by reflection the plane of reflection is the plane of polarization. According to Fresnel's theory, which is that generally received, the vibrations of light polarised in any plane are perpendicular to that plane. The vibrations of a ray reflected at the polarizing angle are accordingly to be regarded as perpendicular to the plane of incidence and reflection, and therefore as parallel to the reflecting surface. Polarised light cannot be distinguished from common light by the naked eye; and for all experiments in polarization two pieces of apparatus must be employed - one to produce polarisation, and the other to show it. The former is called a polariser, the latter an analyser; and every apparatus that serves for one of these purposes will also serve for the other. One such apparatus is the Polariscope.

The usual process in examining light with a view to test whether it is polarised, consists in looking at it through the analyser, and observing whether any change of brightness occurs as the anaylser is rotated. There are two positions, differing by 180 degrees, which give a minimum of light, and the two positions intermediate between these give a maximum of light. The extent of the changes thus observed is a measure of the completeness of the polarisation of light. Very beautiful colours may be produced by the peculiar action of polarized light; as for example, if a piece of selenite (crystallized gypsum) about the thickness of paper is introduced between the polariser and analyser of any polarising arrangement, and turned about in different directions, it will in some positions appear brightly coloured, the colour being most decided when the analyser is in either of the two critical positions which give respectively the greatest light and the greatest darkness. The colour is changed to its complementary by rotating the analyser through a right angle; but rotation of the selenite, when the analyser is in either of the critical positions, merely alters the depth of the colour without changing its tint, and in certain critical positions of the selenite there is a complete absence of colour.

A different class of appearances are presented when a plate, cut from a uni-axial crystal by sections perpendicular to the axis, is inserted between the polariser and the analyser. Instead of a broad sheet of uniform colour, there is exhibited a system of coloured rings, interrupted when the analyser is in one of the two critical positions by a black or white cross. Observations of this phenomenon affords in many cases an easy way of determining the position of the axis of the crystal, and is therefore of great service in the study of crystalline structure. Crystals are distinguished as dextro-gyrate or laevo-gyrate, according as their colours ascend by a right-handed or left-handed rotation of the analyser horizontally. Glass in a state of strain exhibits coloration when placed between a polarizer and analyser, and thus we can investigate the distribution of the strain through its substance. Unannealed glass is in a state of permanent strain. A plate of ordinary glass may be strained by a force applied to its edges by means of a screw. The state of strain may be varied during the examination of the plate by polarised light.

A plate of quartz (a uniaxial crystal) cut at right angles to the optic axis exhibits, when placed between an analyser and polariser, a system of coloured rings like any other uniaxial crystal; but we find that the centre of the rings, instead of having a black cross, is brightly coloured - red, yellow, green, blue, etc, according to the thickness of the plate.
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POLARISCOPE

A polariscope is an optical instrument, various kinds of which have been contrived, for exhibiting the polarization of light, or for examining transparent media for the purpose of determining their polarizing power. The important portions of the instrument are the polarizing and analysing plates or prisms, and these are formed either of natural crystalline structures, such as Iceland-spar and tourmaline, or of a series of reflecting surfaces artificially joined together.
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POLARITY

Polarity is that quality of a body in virtue of which peculiar properties reside in certain points called poles; usually, as in electrified or magnetized bodies, properties of attraction or repulsion, or the power of taking a certain direction; as, the polarity of the magnet or magnetic needle, whose pole is not that of the earth, but a point in the Polar Regions. A mineral is said to possess polarity when it attracts one pole of a magnetic needle and repels the other.
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POLE

Pole is the name given to either extremity of the axis round which the earth revolves. The northern one is called the north pole, and the southern the south pole. Each of these poles is 90 degrees distant from every part of the equator.

In astronomy, the name is given to each of the two points in which the axis of the earth is supposed to meet the sphere of the heavens, forming the fixed point about which the stars appear to revolve.

In a wider sense a pole is a point on the surface of any sphere equally distant from every part of the circumference of a great circle of the sphere; or a point 90 degrees distant from the plane of a great circle, and in a line passing perpendicularly through the centre, called the axis. Thus the zenith and nadir are the poles of the horizon. So the poles of the ecliptic are two points of the sphere whose distance from the poles of the world is equal to the obliquity of the ecliptic, or they are 90 degrees distant from every part of the ecliptic.

In physics, a pole is one of the points of a body at which its attractive or repulsive energy is concentrated, as the poles of a magnet, the north pole of a needle, the poles of a battery.
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POLONIUM

Polonium is a metal radioactive element with the symbol Po.
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POLYAMIDE

Polyamide is a large class of polymers in which the units are linked by an amide group. Polyamides have a high lubricity and moderate strength. They are tough, inexpensive to produce, but have poor dimensional stability due to their tendancy for water absorption. Polyamides are used to make bearings, blow mouldings, and clothing fabric. The synthetic resin nylon is a classic example of a polyamide.
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POLYBASIC ACIDS

Polybasic Acids are those which possess more than one hydrogen atom capable of being replaced by a metal equivalent.
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POLYCARBONATE

Polycarbonate is a thermoplastic polycondensate polymer mass-produced since 1958. It has excellent strength and possesses good dimensional stability, dielectric strength, flame retardancy, and an impact resistance which is the highest among current transparent rigid materials. It is difficult to machine, however.
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POLYCHLORINATED BIPHENYLS

Polychlorinated biphenyls (PCBs) are a family of man-made chemicals that contain 209 individual compounds with varying toxicity. Commercial formulations of PCBs enter the environment as mixtures consisting of a variety of PCBs and impurities. Because of their insulating and non-flammable properties, PCBs have been used widely as coolants and lubricants in transformers, capacitors, and other electrical equipment. The manufacture of PCBs stopped in the USA in October 1977 because of evidence that PCBs accumulate in the environment and may cause health hazards for humans.
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POLYCYCLIC AROMATIC HYDROCARBONS

Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances. PAHs can be man-made or occur naturally. There is no known use for most of these chemicals except for research purposes. A few of the PAHs are used in medicines and to make dyes, plastics, and pesticides. They are found throughout the environment in the air, water, and soil. There are more than 100 different PAH compounds. Although the health effects of the individual PAHs are not exactly alike, the following 15 PAHs are considered as a group: acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(ghi)perylene, benzo(k)fluoranthene, chrysene, dibenz(a,h)anthracene, fluoranthene, fluorene, indeno(1,2, 3-cd)pyrene, phenanthrene, pyrene. As pure chemicals, PAHs generally exist as colourless, white, or pale yellow-green solids.

Most PAHs do not occur alone in the environment (including those found at hazardous waste sites), rather they are found as mixtures of two or more PAHs. They can occur in the air either attached to dust particles, or in soil or sediment as solids. They can also be found in substances such as crude oil, coal, coal tar pitch, creosote, and road and roofing tar. Most PAHs do not dissolve easily in water, but some PAHs readily evaporate into the air. PAHs generally do not burn easily and they will last in the environment for months to years.
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POLYESTER

Polyester is a thermosetting plastic used in the manufacture of synthetic fabrics since 1942. Polyester exhibits excellent dimensional stability but a low resistance to acids and bases.
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POLYETHYLENE

Polyethylene is a thermosetting plastic polymer of ethylene mass produced since 1939. It is an inexpensive plastic widely used in the manufacture of plastic bags, beverage bottles and extruded pipe. Polythene is a proprietory name for polyethylene made by one manufacturer.
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POLYGON

In geometry, a polygon is a plane figure of many angles and sides, or at least of more than four sides. A polygon of five sides is termed a pentagon; one of six sides, a hexagon; one of seven sides, a heptagon, and so on. Similar polygons are those which have their several angles equal each to each, and the sides about their equal angles proportionals. All similar polygons are to one another as the squares of their homologous sides. If the sides, and consequently the angles, are all equal, the polygon is said to be regular; otherwise, it is irregular. Every regular polygon can be circumscribed by a circle, or have a circle inscribed in it.
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POLYGON OF FORCES

In mechanics, polygon of forces is the name given to a theorem which is as follows: If any number of forces act on a point, and a polygon be taken, one of the sides of which is formed by the line representing one of the forces, and the following sides in succession by lines representing the other forces in magnitude, and parallel to their directions, then the line which completes the polygon will represent the resultant of all the forces.
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POLYHEDRON

In geometry, a polyhedron is a body or solid bounded by many faces or planes. When all the faces are regular polygons similar and equal to each other the solid becomes a regular body. Only five regular solids can exist, namely, the tetrahedron, the hexahedron, the octahedron, the dodecahedron, and the icosahedron.
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POLYMER

A polymer is a compound made up of large molecules composed of many repeated simple units.
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POLYMERISM

Polymerism is a particular instance of isomerism. Polymerisation is a name given to the process by which a chemical compound is transformed into another having the same chemical elements combined in the same proportions but with different molecular weights: thus the hydrocarbon amylene, when acted on by strong sulphuric acid, is converted into the polymer paramylene.
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POLYMETHYL METHACRYLATE

Polymethyl methacrylate or acrylic, is a rigid, glassy thermoplastic with a good weight-to-strength ratio and resistance to moisture. Polymethyl methacrylate is used in the manufacture of optical devices, glazing, aircraft windows and similar. As a synthetic fibre, polymethyl methacrylate is often used as a substitute for wool. It was first launched commercially in 1947 but not produced in any great volume until the 1950s. It is a strong, warm fabric that drapes well. It is used to make sweaters and tracksuits, and is also made into linings for boots, gloves, jackets and slippers. Common tradenames for acrylic fibre are Acrilan and Orlon.
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POLYMORPHISM

Polymorphism is the property possessed by certain bodies of crystallizing in two or more forms not derivable one from the other. Thus mercuric iodide separates from a solution in tables belonging to the dimetric system; if these crystals are heated they sublime and condense in forms belonging to the monoclinic system; calcium carbonate exists as calc-spar, which crystallizes in rhombohedral forms, and as aragonite, which crystallizes in trimetric forms.
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POLYSACCHARIDE

A polysaccharide is a long chain of carbohydrate made up of hundreds of linked simple sugars, such as glucose.
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POLYSTYRENE

Polystyrene is a thermoplastic polymer mass-produced since 1930. Polystyrene is easy to mould, it is inexpensive, machines well, and possesses excellent transparency, but is structually weak. It is used to manufacture inexpensive packaging materials, especially when expanded (styrofoam), and in the manufacture of low cost consumer plastic items such as pens and safety razors, CD jewel cases &c.
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POLYTETRAFLUORETHYLENE

Polytetrafluorethylene (PTFE) is a slippery theromplastic polymer with similar properties to polystyrene, except that it has a very wide temperature range and cannot be practically melted. It is chemically inert and as such is resistant to adhesives. Polytetrafluorethylene is used for making gaskets, hoses, insulators, bearings, and for coating metal surfaces in chemical plants and in non-stick cooking vessels - often under the tradename Teflon.
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POLYVINYL ACETATE

Polyvinyl acetate (PVA) is a thermoplastic vinyl polymer formed by the co-polymerization of vinyl chloride and vinyl ethanoate. Polyvinyl acetate is resistant to oil and some chemicals and is widely used to produce plastic sheets, hoses and belts and as a water-based emulsion as an adhesive - 'PVA Glue'.
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POLYVINYL CHLORIDE

Polyvinyl chloride (PVC) is a thermoplastic vinyl polymer mass-produced since 1938. It is an inexpensive plastic with high dielectric strength, outdoor stability, chemical resistance and good moisture stability but a poor resistance to heat. It is widely used in the manufacture of low-cost imitation leather clothing - particularly 'fetish' wear - and in wire and cable insulations.
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POLYVINYLACETATE

Polyvinylacetate is a clear, brittle plastic, resistant to light and heat, readily soluble in alcohols, esters, ketones and chlorinated hydrocarbons. It is commonly encountered mixed in emulsion with polyvinyl alcohol or mixed with cellulose nitrate and softeners to form PVA glue. Polyvinylacetate is also used as a clear lacquer and to make chewing gum.
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PONCEAU 4R

Ponceau 4R (E124) is a red synthetic azo dye used in the UK as a food colouring, but banned in the USA and Norway. Ponceau 4R has been found to cause hyperactivity in children and also allergic reactions.
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POP

In telecommunications, POP (Point of Presence) is a local dial-in point for an Internet Service Provider.
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PORISM

Porism was a name given by ancient geometers to a class of mathematical propositions having for their object to show what conditions will render certain problems indeterminate. Playfair defined a porism thus: 'A proposition affirming the possibility of finding such conditions as will render a certain problem indeterminate, or capable of innumerable solutions'.
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PORT

In computing a port is an 8-bit wide interface between the processor and another system hardware device. In a Personal Computer, each hardware device makes use of a range of port addresses and as such conflicts can occur when two devices use port addresses which overlap.
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PORTLAND CEMENT

Portland cement is the essential constituent in concrete, cement rendering and formerly in asbestos-cement sheeting. Portland Cement is so called from its resemblance in colour to Portland stone. It is made from chalk and gault clay in definite proportions. These materials are intimately mixed with water, and formed into a sludge. This is dried, and when caked is roasted in a kiln till it becomes hard. It is afterwards ground to a fine powder, in which state it is ready for market. This cement is much employed along with gravel or shivers for making artificial stone. A month after it is set it forms a substance so hard as to emit a pinging sound when struck.
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POSITRON

A positron is a positively-charged particle of the same mass as the electron and with a charge equivalent but opposite in sign to that of the electron.
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POSTCODE

Postcode, from AFD Software, is a software system which looks up addresses from
postcodes. The data file is about 18Mb, which includes the indices which reduce typical search times to less than one second.
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POSTSCRIPT

PostScript was a groundbreaking Page Description Language (PDL), based on work originally done by John Gaffney at Evans and Sutherland in 1976, evolving through 'JaM' ('John and Martin', Martin Newell) at XEROX PARC, and finally implemented in its current form by John Warnock et al. after he and Chuck Geschke founded Adobe Systems Incorporated in 1982. PostScript gets its leverage by using a full programming language, rather than a series of low-level escape sequences, to describe an image to be printed on a laser printer or other output device (in this it parallels EMACS, which exploited a similar insight about editing tasks). It is also noteworthy for implementing on-the fly rasterisation, from Bezier curve descriptions, of high-quality fonts at low (e.g. 300 dpi) resolution (it was formerly believed that hand-tuned bitmap fonts were required for this task).
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POT METAL

Pot Metal is an inferior kind of brass comprised of 10 parts of copper to 6 or 8 parts of lead. It was used for making large vessels employed in the arts and in some stained glass.
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POTASH

Potash was the name originally given to the product obtained when a solution of vegetable ashes is boiled with quicklime in iron pots, and the residue ignited. It derives its name from the ashes, and the pots (called potash kettles) in which the solution was evaporated. In the crude state it is impure potassium carbonate, and when purified is known as pearl-ash. It is used in the making of glass and soap, and large quantities of it are produced from certain 'potash minerals' (especially carnallite), instead of from wood ashes. The name potash was later often given to potassium hydroxide, which is also termed caustic potash. This is either prepared from the carbonate or by the electrolysis of potassic chloride solution, using mercury as the cathode. It is a white solid, usually sold in lumps or in the form of sticks, dissolves readily in water, and has a strongly alkaline reaction. It changes the colour of many natural colouring matters, eg turns pink litmus blue, and eats or corrodes most animal and vegetable tissues. It rapidly absorbs moisture and carbon dioxide from the atmosphere. It neutralizes all acids, yielding the corresponding potassic salts, and is largely made use of in chemical laboratories and in several of the arts. Crude potash is also used in the manufacture of soft soaps. It is fusible at a heat of 300 degrees, and is volatilized at low ignition. It was used in surgery under the name of lapis infernalis or lapis causticus for destroying warts, fungoid growths, etc, and was also applied beneficially to the bites of dogs, venomous snakes, etc.
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POTASSIUM

Potassium is a silver-white, light, soft, low-melting, univalent metallic element of the alkali group, it occurs abundantly in nature especially combined in minerals. It has the symbol K. Potassium was discovered by Davy in 1807, and was one of the first-fruits of his electro-chemical researches. Next to lithium potassium is the lightest metallic substance known, its specific gravity being 0.865 at the temperature of 60 degrees. At ordinary temperatures it may be cut with a knife and worked with the fingers. At 32 degrees it is hard and brittle, with a crystalline texture; at 50 degrees it becomes malleable, and in lustre resembles polished silver; at 150 degrees it is perfectly liquid.

It is usually manufactured by the electrolysis of the hydroxide or chloride, and is an important constituent of saltpetre, common alum, and most manures. Potassium combines very readily with oxygen, and is capable of abstracting it from various oxygen compounds. A freshly-exposed surface of potassium instantly becomes covered with a film of oxide. The metal must therefore be preserved under a liquid free from oxygen, petroleum being generally employed. It decomposes cold water with great readiness, hydrogen gas is evolved and burns with a violet-coloured flame, due to potassium vapour which is present; the other product is caustic potash, which dissolves in the water.
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POTASSIUM ANTIMONYL TARTRATE

Potassium antimonyl tartrate (tartar emetic) is a poison formerly used in small quantities to induce sweating and as an emetic. It is obtained by boiling antimony oxide with a solution of cream of tartar. It forms rhombic efflorescent crystals, is fairly soluble in water and has an unpleasant taste.
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POTASSIUM BENZOATE

Potassium benzoate is a chemical antimicrobial (it kills mold, yeast and bacteria) used as a food preservative, especially as an alternative to sodium benzoate where a lower sodium content is required. Potassium benzoate is a white coloured, granulated solid, almost odourless, which dissolves readily in water and has a tangy taste.
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POTASSIUM BISULPHATE

Potassium bisulphate (potassium acid sulphate) is a colourless, crystalline water-soluble substance used chiefly in the conversion of tartrates to bitartrates.
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POTASSIUM BROMATE

Potassium bromate is a white, crystalline, water-soluble powder used chiefly as an oxidising agent and as an analytical reagent.
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POTASSIUM BROMIDE

Potassium bromide (bromide) is a white, crystalline, water-soluble powder. It has a bitter, saline taste and is used in the manufacture of photographic papers and plates and as a sedative.
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POTASSIUM CARBONATE

Potassium carbonate is a white, granular, water-soluble substance used chiefly in the manufacture of soap, glass and potassium salts.
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POTASSIUM NITRATE

Potassium nitrate (saltpetre, nitre, potassioc nitrate) is a white bitter tasting substance used in gunpowder, as an oxidising agent, for pickling meat, in medicine, in metallurgy and the arts. It is produced by the action of microbes in soils containing potash and nitrogenous organic matters, and forms an efflorescence upon the surface in several parts of the world, and especially in the East Indies, whence much potassium nitrate is traditionally derived. In some parts of Europe it was prepared artificially from a mixture of common mould or porous calcareous earth with animal and vegetable remains containing nitrogen. It is also manufactured on a large scale by crystallization from a hot solution of potassium chloride nitrate of soda. It is a colourless salt with a saline taste, and crystallizes in six-sided prisms. It is employed in chemistry as an oxidizing agent and in the formation of nitric acid. Its chief use in the arts is in the making of gunpowder.
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POTASSIUM OXALATE

Potassium oxalate is a colourless, crystalline water-soluble substance. It is toxic, and is used as a bleaching agent and in medical tests as an anticoagulant.
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POTASSIUM SORBATE

Potassium sorbate is a potassium salt version of sorbic acid, a polyunsaturated fat used to inhibit mould growth. It was first discovered by the French in the 1850's, having been derived from the rowan tree. It is widely used in the food industry. It has been found to be non-toxic even when taken in large quantities, and breaks down in the body into water and carbon dioxide in the Kreb's Cycle.
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POTASSIUM THIOCYANIDE

Potassium Thiocyanide is a sulphocyanate. It is colourless, easily dissolvable crystals used in dyeing.
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POTENTIAL ENERGY

Potential energy is the energy something has by reason of its position or state.
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POUDRE BLANCHE CORNIL

Poudre Blanche Cornil is a Danish explosive used in coal mining comprised of ammonium nitrate, alkali nitrate, nitro-naphthalene and lead chromate.
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POUNDAL

The poundal is the imperial unit of force, now replaced in the SI system by the Newton. One poundal equals 0. 1383 Newtons. It is defined as the force necessary to accelerate a mass of one pound by one foot per second per second.
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POWER

In physics, power is defined at the rate of doing work, and is expressed by the equation: Average
Power = Work done/Time taken.
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POWERNOTE MMX

The Powernote MMX was a laptop PC from Powercom. It was based upon an Intel Pentium MMX processor clocked at 166 Mhz and was supplied with 32 mb of RAM, 810 mb EIDE hard disk, CD-ROM, 1.44 mb floppy drive and a Neomagic 2093ZV graphics accelerator.
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POWERPOINT

Microsoft PowerPoint is one of the most useful presentation programs available. Its unique approach gives you the ability to create overheads, 35mm slides, notes for yourself, and handouts for your audience. PowerPoint lets you plan, compose, and create an entire presentation in a simple, structured manner. PowerPoint lets you create, manage, edit, and manipulate slides. Powerful word processing capabilities and some drawing capabilities are built into the program. The product lets you integrate elements created elsewhere. When creating presentations using the Slide Master, you can create a standard format template, including text and graphics, for all slides. Free-form design lets you integrate what you need on a slide including typeset-quality text, diagrams, graphs, and illustrations. Graphics from the clipboard or scrapbook can be integrated into a PowerPoint slide or you can use the Paste From command to import information from files of other applications. The program's text capabilities include multiple fonts, sizes, and styles.

PowerPoint also includes a spell checker and a find-and-replace text command that works with slides, note pages, and handout pages. You can also create diagrams with its drawing tools which include lines, ellipses, rectangles, and rounded rectangles. The slide-management tools let you rearrange and refine your presentation. A slide sorter displays your slide show on-screen in thumbnail sketch view. You can delete, copy, and rearrange slides and add slides from other presentations. You can also edit the slides by double clicking on them. A slide show feature lets you preview your slides in sequence if you want to rehearse your presentation. Speaker's notes and audience handouts (with two, three, or six slides per page) can be created at the same time you create slides through a user-definable notepage associated with each slide. You can output slides to a printer, slide-making device, or the Genigraphics slide making bureau (a driver is included).
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PRASEODYMIUM

Praseodymium is a metal element with the symbol Pr used as a pigment in glass.
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PRECESSION OF THE EQUINOXES

The Precession of the equinoxes is a slow motion of the line of intersection of the celestial equator or equinoctial and the ecliptic, which causes the positions occupied by the sun at the equinox (the equinoctial points) to move backward or westward at the mean rate of 50.25 minutes per year. This motion of the equinox along the ecliptic carries it, with reference to the diurnal motion, continually in advance upon the stars; the place of the equinox among the stars, with reference to the diurnal motion, thus precedes at every subsequent moment that which it previously held, hence the name. This sweeping round in the heavens of the equinoctial line indicates a motion of the axis of rotation of the earth, such that it describes circles round the poles of the ecliptic in 25,791 years. Nutation is a similar, but much smaller gyratory motion of the earth's axis, whose period is about nineteen years. From these two causes in combination the axis follows a sinuous path, instead of a circle, about the pole of the ecliptic. Nutation causes the equinoctial points to be alternately in advance of and behind their mean place due to precession by 6.87 minutes.
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PRECIPITATE

In chemistry, precipitate is the name given to the solid particles often formed when two clear liquids are mixed. The nature of the precipitate formed by the addition of a certain reagent to an aqueous solution often enables us to say what chemical is present in the solution. Red oxide of mercury is often called red precipitate.
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PREPEND

In computing, prepend means to add or insert an element or elements at the start of a list, table, array, or file, as distinct from the more usual append which is to add elements to the end of an existing list, table, array, or file.
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PRESERVING JARS

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A preserving jar is a glass jar covered with a glass cap seated on a flat rubber ring used for keeping fruit in an eatable condition for a long time. Clean fruit and water are placed in the jar, leaving a small air space at the top. Several of these jars are placed in a large vessel of cold water, which is then slowly brought to the boil. During this process the glass caps with their rubber rings are loosely held in position by a metal screw cap. About 10 minutes boiling is generally sufficient to sterilise the fruit and to cause air to be driven from the jars by steam from the water inside. The screw caps are then tightened and the jars removed from the water. After cooling, the space at the top of the jars contains only water vapour at low pressure. As a result, the glass cap is then firmly pressed down by atmospheric pressure. No bacteria-laden air can afterwards enter, and so the contents remain in good condition for a long period. When the jars have cooled the presence of the metal cap is not strictly necessary, as the seal is
now maintained by atmospheric pressure.
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PRESSURE

In physics, pressure is defined as: The force acting normally (perpendicularly) per unit area.
Pressure can be represented by the equation: Pressure = Thrust / Area. Thus, given an object of a static weight, the pressure exerted by that object varies with the area to which the pressure is applied. For example, a brick exerts less pressure upon an area when lying on its large side than when standing on its small end.
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PRIMARY COLOUR

A primary colour is one of the three basic lights of red, green and blue. A primary pigment is one of the three basic pigment colours of red, yellow and blue. From the mixing of these three colours different colours can be produced, though it should be strongly noted that mixing different colours of light will produce a different colour than is produced from mixing the same coloured pigments, for example mixing the three primary coloured lights in equal proportions will produce a white light, while mixing the same three coloured pigments in the same proportions will produce a black pigment.
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PRIME CONDUCTOR

A prime conductor is that part of an electric machine from which sparks are usually taken.
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PRIME NUMBER

A prime number is a number which can be divided exactly by no number except itself and unity.
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PRIMING

In steam-engines, priming is the entrance of water spray along with steam into the cylinder of an engine. It always causes great annoyance. The use of muddy water, insufficient steam-room, carelessly constructed flues and pipes, etc, in the boiler, give rise to priming. Superheating the steam is one remedy. Priming valves, a species of spring valves, fitted to the cylinder, are so adjusted as to eject priming by the action of the piston.
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PRINCE'S METAL

Prince's Metal (or Prince Rupert's Metal) is imitation gold made from copper and zinc.
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PRINCIPLE

In chemistry, a principle is component part or element on which the essential or characteristic properties of a substance depend.
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PRISM

A prism is a solid figure that is essentially triangular in shape and made of a transparent material. They are used in physics to deviate or disperse a ray in optical instruments or laboratory experiments. If a narrow beam of white light is passed through a prism it is split into a range of colours. The light is split because each of the colours is refracted by a different amount, because each is light of a different wavelength.
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PROBABILITY

In algebra probability is the mathematical investigation of chances; the ratio of the number of chances by which an event may happen, to the number by which it may both happen or fail. If an event may happen in a ways and fail in b ways, and all these ways are equally likely to occur,
the probability of it happening is a / (a+b) and the probability of it failing are b / (a+b). 'Certainty' being represented by unity. When the probability of the happening of an event is to the probability of its failing as a to b, the fact is expressed in popular language thus the 'odds' are a to b for the event, or b to a against the event. If there are three events such that one must happen, and only one can happen, and suppose the first event can happen in a ways, the second in b ways, and the third in c ways, and that all these ways are equally likely to occur, then it is evident that the probability of the happening of the first event is a/ (a+b+c) and of its failing (b+c) / (a+b+c).
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PROC

In Unix, proc is a pseudo-filesystem that is used as an interface to kernel data structures rather than reading and interpreting /dev/kmem. In particular, its files do not take disk space.
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PROCESS WHITE

Process white is an opaque water-mixed white prepared from blanc fixe and used by designers and commercial artists.
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PROCOMM

ProComm was a shareware communications program for the IBM PC usually used for accessing dial-up services such as BBS.
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PRODUCER GAS

Producer Gas is a gas made in a special furnace or 'producer', and generally intended to be used as fuel on the spot. It is made by the incomplete combustion of coal, coke, charcoal, or certain other fuels, a stream of air and steam being made to pass through the burning fuel and a gaseous mixture being given off, which was largely used as fuel in various manufacturing operations. In the late 19th century a form of producer was introduced to supply gas directly for a gas-engine, the gas before being drawn into the motor being passed through a cooler and then sucked into a scrubber and purified.
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PRODUCT DETECTOR

In radio, a product detector is a beat frequency oscillator with enhancements for improved SSB and CW reception.
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PROGRESSION

In mathematics, progression is a regular or proportional advance in increase or decrease of numbers. Continued arithmetical progression is when the terms increase or decrease by equal differences. Thus, 2, 4, 6, 8, 10, and 10, 8, 6, 4, 2, increase and decrease by the difference 2. Geometrical progression is when the terms increase or decrease in a certain constant ratio, as 2, 4, 8, 16, 32, 64, and 64, 32, 16, 8, 4, 2, which respectively increase and decrease by a continual multiplication or division by 2. Harmonical progression is progression in harmonical proportion, or such that of any three consecutive terms the first is to the third as the difference between the first and second to the difference between the second and third.
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PROLOG

Prolog is a computer programming language used mainly for artificial intelligence.
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PROMETHIUM

Promethium is a metal element with the symbol Pm.
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PRONY BRAKE

In mechanics, a Prony brake or Prony's dynamometer (named after the French engineer, Baron de Prony), is a device for determining the power of a machine by applying a brake to it and measuring the work done against a frictional torque, or tendency to return to a state of rest.
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PROPANE

Propane is a gaseous hydrocarbon found in petroleum. It has the formulae c3h8.
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PROPELLER

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The propeller (properly screw-propeller) is an apparatus which, being fitted to ships and aeroplanes and driven by steam or a combustion engine, propels them through the water or air, and which, in its various forms, is a modification of the common screw. Originally a ship's propeller thread had the form of a broad spiral plate, making one convolution round the spindle or shaft, but later it consisted of several distinct blades, forming portions of two, three, or four threads. In shape the propeller blades vary considerably, and propellers with two blades have been little used on ships since about 1900, though are popular on aircraft.

The position for the propeller in a single-screw ship is immediately before the rudder, the shaft passing parallel to the keel into the engine-room, where it is set in rapid motion by the engines. This rotatory motion in the surrounding fluid, which may be considered to be in a partially inert condition, produces, according to the well-known principle of the screw, an onward motion of the vessel more or less rapid, the forward 'thrust' of the screw being directly taken by a 'thrust-block' firmly connected with the structure of the ship. The shaft on leaving the ship passes through the stern-tube, where it is surrounded by packing to prevent water from entering the ship. The blades of the propeller may be joined individually to the 'propeller-boss', a spherical protuberance at the end of the shaft; or boss and blades may be cast in one, and the whole connected to the shaft. Cast-steel or bronze is the material frequently employed.

Twin-screws and twin-shafts are in common use, one on each side of the centre-line of the vessel, the screws and ends of the shafts being supported by brackets projecting towards the stern. Three shafts and propellers are also employed, and there may be more than one propeller on each shaft.


The successful introduction of the screw-propeller is due to Sir F P Smith and to Ericsson, who both independently and about the same time (1838) secured patents. Numerous modifications of the screw-propeller have been proposed and adopted since it was first introduced, and it had quite superseded the paddle-wheel for seagoing vessels by 1900.
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PROPORTION

In mathematics, proportion is the equality or similarity of ratios, ratio being the relation which one quantity bears to another of the same kind in respect of magnitude; or proportion is a relation among quantities such that the quotient of the first divided by the second is equal to the quotient of the third divided by the fourth. Thus 5 is to 10 as 8 is to 16; that is, 5 bears the same relation to 10 as 8 does to 16. Proportion is expressed by symbols, thus: a: b:: c : d, or a:b = c: d. The above is sometimes called geometrical proportion in contradistinction to arithmetical proportion, or that in which the difference of the first and second is equal to the difference of the third and fourth.

Harmonical or musical proportion is a relation of three or four quantities such that the first is to the last as the difference between the two first is to the difference between the two last; thus 2, 3, 6 are in harmonical proportion, for 2 is to 6 as 1 is to 3. Reciprocal or inverse proportion is an equality between a direct and a reciprocal ratio, or a proportion in which the first term is to the second as the fourth is to the third, as 4:2 :: 3:6 inversely, that is as 1/3:1/6.
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PROPORTIONAL COMPASSES

Proportional Compasses are compasses used for reducing or enlarging drawings, having the legs crossing so as to present a pair on each side of a common pivot. By means of a slit in the legs, and the movable pivot, the relative distances between the points at the respective ends may be adjusted at pleasure in the required proportion.
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PROPYL GALLATE

Propyl gallate (n-propyl ester of 3,4,5-trihydroxybenzoic acid) is a white to creamy-white coloured, crystalline, odourless solid, soluble in water, ethanol and fat, with a slightly bitter taste, used as an anti-oxidant in processed foods.
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PROPYLENE GLYCOL

Propylene glycol is a colourless viscous hydroscopic sweet-tasting compound used as an antifreeze and brake fluid, and in some cosmetics. It is also known as 1,2-dihydroxypropane.
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PROPYLENE GLYCOL MONOMETHYL ETHER

Propylene glycol monomethyl ether is a glycol ether primarily used in the manufacture of lacquers and paints, as an anti-freeze in industrial engines, a tailing agent for inks used on very high-speed presses, a coupling agent for resins and dyes in water-based inks, and a solvent for celluloses, acrylics, dyes, inks, and stains. It is also used in cleaning products such as glass and rug cleaners, carbon and grease removers, and paint and varnish removers; and in pesticide formulations as a solvent for applications to crops and animals.
Propylene glycol monomethyl ether is a colourless liquid with a sweet ether-like odour and bitter taste. It is soluble in water, ether, acetone, and benzene. It is also known as 1-methyl-2-hydroxypropane.
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PROPYLENE OXIDE

Propylene oxide is a colourless liquid with an ether-like odour that is used mainly as a chemical intermediate in the production of polyurethane polyols, which are used to make polyurethane foams, coatings, and adhesives. It is used in the manufacture of propylene glycol, which is used in fibreglass-reinforced plastics, foods, cosmetics, pharmaceuticals, cigarette tobacco, packaging materials, dyes, and hydraulic fluids. It is also used in the preparation of glycol ethers, dipropylene glycol, industrial polyglycols, lubricants, surfactants, oil demulsifiers, isopropanolamines, and as a solvent and soil sterilant. It is used in fumigation chambers for the sterilization of packaged foods; as a stabilizer for methylene chloride, fuel, and heating oils; in treating wood for termite resistance; as an acid scavenger and pH control agent; for removing residual catalysts from crude polyolefins; in fuel-air explosives in munitions; and as a component of Zeospan, a polyether rubber.

Propylene oxide is a volatile, flammable liquid that is soluble in water, alcohol, and ether. It is highly dangerous when exposed to heat or flame. It has a violent reaction with hydrogen chloride, chlorosulphonic acid, hydrogen fluoride, and oleum. It should not be stored in the presence of acids, bases, chlorides of iron, aluminium, and tin, or peroxides of iron and aluminium; any of these may cause violent polymerisation.

Propylene oxide is miscible with most organic solvents, and forms a two-layer system with water. It is incompatible with anhydrous metal chlorides, iron, strong acids, caustics, and peroxides, and reacts vigorously with oxidizing materials. When exposed to flame, propylene oxide can explode. Polymerisation may occur due to high temperatures or contamination with alkalis, aqueous acids, amines, and acidic alcohols.

Propylene oxide is also known as epoxypropane; 1,2-epoxypropane; methyl ethylene oxide; methyl oxirane; propene oxide; and 1,2-propylene oxide. Derivatives of
propylene oxide are polyether polyols; propylene glycol; di- and tripropylene glycol; poly (propylene glycol)s; surfactants; glycol ethers; and isopropanolamines.
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PROTACTINIUM

Protactinium is a rare actinide element with the symbol Pa.
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PROTECTED MODE

In Personal Computing, protected mode is an operational mode that an 80286 or later Intel processor can operate in. Protected mode was developed with the 80286 CPU to allow multi-tasking programs to operate on a Personal Computer. When a processor is operating in protected mode, each running program is allocated an area of memory. Any program attempting to access memory outside its allocation generates an exception error which forces the offending program to be terminated without it overwriting memory in use by another program. Operating systems such as Unix, Windows 95, Windows 98, Windows NT, Windows 2000 and Windows XP all utilise protected mode.
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PROTEIN

Protein is a long chain molecule made up of amino acids joined by peptide bonds.
Protein forms the structural material of bodily tissues.
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PROTIUM

Protium is an isotope of hydrogen.
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PROTON

A proton is a positively charged sub-atomic particle.

Proton was the name of a series of Soviet scientific satellites, the first launched in July 1965, designed primarily to study cosmic particles of super-high energies.
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PROTRACTOR

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A protractor is a mathematical instrument for laying down and measuring angles on paper.
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PROXY CACHE

A proxy cache is a computer cache system on a network, such as the Internet, often located near to a network gateway and used to reduce the bandwidth required over expensive dedicated internet connections. Proxy caches serve many users with cached files from many remote servers. Their primary usefulness is in caching files requested by one user for later retrieval by another. Some
proxy caches are part of cache hierarchies, in which a cache can ask neighbouring caches for a requested file to reduce the need to fetch the file directly from it's source.
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PRUSSIAN BLUE

Prussian blue (also formerly known as Berlin Blue) is a blue pigment discovered by Diesback (known as the Prussian) of Berlin in 1710. It is prepared by precipitating a ferric salt, such as ferrous sulphate, with a solution of potassium ferrocyanide. Prussian blue varies from a slightly greenish blue to a blue tinged with violet and has a characteristic bronze lustre. Prussian blue has an intense colour and great staining strength but its noted for its transparency. Prussian blue is resistant to acid, but vulnerable to alkali.
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PRUSSIAN BROWN

Prussian Brown or cupric ferrocyanide is a brown pigment obtained by precipitating a solution of yellow prussiate of potash with blue vitriol (copper sulphate) solution. When washed and dried it is equal to madder, and possesses greater permanency.
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PSEARCH

Psearch by Patri-Soft is an extension to the DOS computer operating system. You provide words or phrases, and it will scan directories to find files containing the text. Extensive file selection and pattern matching are provided. It provides an intelligent display of found text with a scroll back and program launcher. Psearch saves search results for later review. Psearch was recommended in PC World as one of the Best of Shareware products in 1990.
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PSYCHROMETER

Psychrometer is a term applied to an instrument for measuring the tension of the aqueous vapour in the atmosphere; a form of hygrometer.
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PTOMAINES

Ptomaines or toxines are a group of alkaloids characterized by their highly poisonous properties. They are produced during the decay of animal matter, and are usually present in putrid meat (sometimes in tinned meat). If this is eaten, serious poisoning often results. They all possess basic properties and dissolve in acids.
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PUBERTY

Pu'berty is the period in both male and female marked by the functional development of the generative system. In males it usually takes place between the ages of thirteen and sixteen; in females somewhat earlier; and, as a rule, in very warm climates puberty is reached somewhat sooner than elsewhere. In males puberty is marked externally by the deepening of the voice, the first appearance of the beard, greater firmness, fulness of body, etc; in females, by the enlargement of the breasts and by the general rounding out of the frame, and most unequivocally of all by the commencement of menstruation.
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PUBLISHER'S PAINTBRUSH

Publisher's Paintbrush by ZSoft is a full-featured freehand-painting program that offers all the standard capabilities found in other painting programs (it is a superset of PC Paintbrush), plus some capabilities desktop publishers will find invaluable. When creating or scanning a 300-dpi image, a 62 screen image is produced. Rather than editing the image screen-by-screen, you can zoom out and work on the multiscreen image in its entirety. The editing you do in normal mode can be handled in the zoom out mode.

The program lets you take full advantage of scanners, laser printers, and desktop publishing programs. Used with scanners, Publisher's Paintbrush gives you control over brightness and contrast, the resolution at which you want to scan the image, and the location on the page you want to scan. Publisher's Paintbrush lets you define the exact dimensions on the page of your scanned image which greatly reduces the amount of time it takes to scan and edit images.

Publisher's Paintbrush has very strong typography capabilities, making it ideal for creating illustrations that require sophisticated type. Type sizes are adjustable to any point size. You can slant the type to any angle to get curved type, italicise it as much or as little as you would like, and set the line and character spacing. Leading and kerning are also adjustable. Publisher's Paintbrush lets you edit at the pixel level with 300 dpi full-page output.
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PUFFER

Puffer by Kent Briggs is a password-based data file and e-mail encryption utility for Microsoft Windows. It allows you to keep your personal, business, and electronic transmitted data private.
Puffer uses the highly rated Blowfish algorithm for fast, secure encryption and the Secure Hash Algorithm (SHA) for key generation. Three output formats are supported including binary, self- extracting executables, and 7-bit text for Internet e-mail.
Puffer also includes a three-pass, secure file wipe feature.
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PUG-MILL

A pug-mill is a machine for mixing and tempering clay. It consists of a hollow metal cylinder, generally set upright, with a revolving shaft in the line of its axis, carrying a number of knives projecting from it at right angles, and arranged in a spiral manner. The clay is thrown in at the top of the cylinder, and by the revolution of the shaft is brought within the action of the knives, by which it is cut and kneaded in its downward progress, and finally forced out through a hole in the bottom of the cylinder.
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PUGGING

Pugging is the process of mixing a pigment with a medium in such a way that the pigment forms a thick paste.
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PUK

PUK stands for Personal Unblocking Key. It is a code number that is associated with a mobile phone SIM card. If the sim card becomes blocked, by entering the wrong PIN code a number of times, or if the phone has been locked after being reported lost or stolen, it must be unblocked by entering the OUJ code. The PUK code can usually be obtained from the network provider, for example the O2 network can supply the PUK code if you provide them with the mobile phone telephone number. If you enter the wrong PUK code too many times (typically you have ten attempts) then you will usually have to replace the SIM card.
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PULLEY

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In engineering, a pulley is a wheel for transmitting power from, or imparting it to, different parts of machinery, or for changing the direction of motion by means of a cord, belt or rope.

A pulley takes the form of a small wheel movable about an axle, and having a groove cut in its circumference over which a cord passes. The axle is supported by a kind of case or box called the block, which may either be movable or fixed to a firm support. The pulley is one of the six simple machines or mechanical powers, and is used for raising weights. A single pulley serves merely to change the direction of motion, but several of them may be combined in various ways, by which a mechanical advantage or purchase is gained, greater or less, according to their number and the mode of combination. The advantage gained by any combination or system of pulleys is readily computed by comparing the velocity of the weight raised with that of the moving power, according to the principle of virtual velocities. The friction, however, in the pulley is great, particularly when many of them are combined together.

A pulley is said to be fixed when the block in which it turns is fixed, and it is said to be movable when the block is movable. In the single fixed pulley there is no mechanical advantage, the power and weight being equal. It may be considered as a lever of the first kind with equal arms. In the single movable pulley where the cords are parallel there is a mechanical advantage, there being an equilibrium when the power is to the weight as 1 to 2. It may be considered as a lever of the second kind, in which the distance of the power from the fulcrum is double that of the weight from the fulcrum.

In a system of pulleys in which the same string passes round any number of pulleys, and the parts of it between the pulleys are parallel, there is an equilibrium when the power is to the weight as 1 to the number of strings at the lower block. In a system in which each pulley hangs by a separate cord and the strings are parallel there is an equilibrium when the power is to the weight as 1 to that power of 2 whose index is the number of movable pulleys.


Whatever be the mechanical arrangement of the pulleys and of the ropes the principle of all pulleys is the same, namely, the transmission of the tension of a rope without sensible diminution so as to obviate the loss of force consequent on rigidity. The term pulley is used indifferently to denote either a single sheave or the complete block and its sheaves.

In machinery, a pulley is a wheel, generally with a nearly flat face, which being placed upon a shaft transmits power to or from the different parts of the machinery, or changes the direction of motion by means of a belt or band which runs over it.
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PULSE CODE MODULATION

Pulse Code Modulation (PCM) is the standard method of digitally encoding audio. It is the basic uncompressed data format used to record audio CDs, and also by computer formats such as Windows .wav and Apple AIFF.
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PULSE MODULATION

Pulse modulation is a radio modulation method in which the timing, amplitude, and/or spacing of pulses of a transmitter's carrier are varied in order to convey information.
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PULSOMETER

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A pulsometer is an instrument of the pump kind for raising water, especially when that liquid is mixed with solid matter. It acts by the condensation of waste steam sent into a reservoir, the water rushing up into the vacuum formed by the condensation. It consists essentially of a double chamber, or two connected chambers, having a ball-valve at the top (which shuts either chamber alternately) and clack-valves at the bottom. Steam is admitted to one of the chambers and presses out the water contained there through a pipe to be carried away. Condensation then taking place a vacuum is formed, and the ball falls over and closes the opening through which the steam entered, and water flows up through the clack-valves and again fills the chamber. The steam in the meantime is now acting upon the water in the adjoining chamber, condensation then taking place there, the ball falls back to that side, and the operations go on alternately, the result being a steady stream of water sucked into one chamber after another, and then forced out and upwards by the steam.
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PUMP

A pump is a contrivance for raising liquids or for removing gases from vessels. Though the forms under which the hydraulic pump is constructed, and the mode in which the power is applied, may be modified in a great variety of ways, there are only four which can be considered as differing from each other in principle. These are the sucking or suction pump, the lift-pump, the force-pump, and the rotary or centrifugal pump.

Of these the suction or common household pump is most in use, and for ordinary purposes the most convenient. In the usual construction of this pump a piston is fitted to work air-tight within a hollow cylinder or barrel. It is moved up and down by a handle connected with the piston-rod, and is provided with a valve opening upwards. At the bottom of the barrel is another valve also opening upwards, and which covers the orifice of a tube called the suction-tube, fixed to the bottom of the barrel, and reaching to the bottom of the well from which the water is to be raised. When the piston is drawn up from the bottom of the barrel the air below is rarefied, and the pressure of the external air acting on the surface of the water in the well, causes the water to rise in the suction-tube until the equilibrium is restored. After a few strokes the water will get into the barrel, the air below the piston having escaped through the piston-valve. By continuing, the water will get above the piston and be raised along with it to the cistern at the top of the barrel, where it is discharged by a spout.

The lift-pump has also two valves and a piston, both opening upwards; but the valve in the cylinder instead of being placed at the bottom of the cylinder is placed in the body of it, and at the height where the water is intended to be delivered. The bottom of the pump is thrust into the well a considerable way, and the piston being supposed to be at the bottom, as its valve opens upwards there will be no obstruction to the water rising in the cylinder to its height in the well. When the piston is drawn up its valve will shut, and the water in the cylinder will be lifted up; the valve in the barrel will be opened, and the water will pass through it and cannot return as the valve opens upwards; another stroke of the piston repeats the same process, and in this way the water is raised from the well: but the height to which it may be raised is not in this as in the suction-pump limited to 32 or 33 feet.

The force-pump differs from both of these in having its piston solid, or without a valve, and also in having a side pipe with a valve opening outwards, through which the water is forced to any height required, or against any pressure that may oppose it. In such pumps the plunger or solid piston is frequently employed instead of the ordinary piston. The plunger works airtight through a stuffing-box at the top of the barrel, and on being raised produces a vacuum in the pump-barrel into which the water rushes by a pipe and is discharged, on the descent of the plunger through another pipe, the valves serving to intercept the return of the water at each stroke. A side pipe however, requires the addition of an air-vessel.

'Double-acting' pumps are often employed for household purposes.

Centrifugal pumps are universally employed wherever the lift is not too great, and the quantity of water is considerable. A wheel, shaped like an ordinary fan, has passages leading from its centre to its circumference; it is made to rotate very rapidly in a casing. Its circumference communicates with a delivery pipe, and its centre with a pipe leading to the water which is to be pumped. The rapid revolution of the wheel causes by centrifugal action a constant flow of water from centre to circumference of the wheel; and in this way the water is sucked up to the centre of the wheel, and leaves the circumference by the eduction pipe. Centifrugal pumps are used in washing machines and spin-dryers.
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PUNCH

A punch is a tool worked by pressure or percussion, employed for making apertures, in cutting out shapes from sheets or plates of various materials, in impressing dies, etc. Punches are usually made of steel, and are variously shaped at one end for different uses. They are solid for stamping dies, etc, or for perforating holes in metallic plates, and hollow and sharp-edged for cutting out blanks, as for buttons, steel-pens, jewelry, and the like.
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PURILASE

Purilase are enzymes used to assist the breakdown of starch in effluent treatment plants.
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PURISOL

Purisol is a specialised macro-nutrient solution to enhance performance in biological effluent treatment plants.
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PURPURATE

In chemistry, a purpurate is a salt of purpuric acid.
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PUS

Pus is a yellowish liquid that forms in the body as a result of bacterial infection.
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PUTTY

Putty is a kind of paste or cement compounded of whiting or soft carbonate of lime and (usually) linseed oil, beaten or kneaded to the consistency of dough. It is used by glaziers for fitting window panes and also by house painters to stop up holes in wood-work prior to painting.
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PUTTY-POWDER

Putty-powder is a pulverised oxide of tin sometimes mixed with oxide of lead. It is extensively used for polishing and other purposes in glass and marble works.
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PYRAMID

In geometry a pyramid is strictly a solid contained by a plane triangular, square, or polygonal base, and other planes meeting in a point. This point is called the vertex of the pyramid; and the planes which meet in the vertex are called the sides, which are necessarily all triangles, having for their bases the sides of the base of the pyramid. Every pyramid is one-third the solid content of a prism that has the same base and altitude as the pyramid. Pyramids are denominated triangular, square, pentagonal, etc, according as the base is a triangle, a square, a pentagon, etc.
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PYRHELIOMETER

The pyrheliometer is an instrument devised by Pouillet for measuring the intensity of the heat of the sun. It consists of a shallow cylindrical vessel of thin silver or copper, containing water or mercury in which a thermometer is plunged. The upper surface of the vessel is covered with lamp- black so as to make it absorb as much heat as possible, and the vessel is attached to a support in such a way that the upper surface can be always made to receive the rays of the sun perpendicularly.
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PYRIDINE

Pyridine is a basic compound occurring in coal tar and in the oil obtained by the distillation of bones. It is the parent substance of a large number of derivatives, including some of the natural alkaloids, such as nicotine and piperine. Pyridine is sometimes used for denaturing alcohol, so as to render it unfit to drink.
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PYRO-ELECTRICITY

Pyro-electricity is a name given to electricity produced by heat, as when tourmaline becomes electric by being heated between 10 and 100 degrees Centigrade.
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PYROCATECHIN

Pyrocatechin is ortho-dihydroxy-benzene. It is formed when catechin and similar bodies are distilled, and is prepared from guaicol, occurring in beech tar by heating with hydriodic acid. Pyrocatechin forms white crystals that dissolve in water. Its solution is turned green by ferric chloride, and acts as reducing agent, particularly in alkaline solution. It has been employed as a photographic developer.
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PYROCOLLODION

Pyrocollodion is a highly nitrated, soluble gun-cotton explosive. It was formerly used by the United States.
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PYROGALLIC ACID

Pyrogallic Acid (pyrogallol) is an acid obtained by the dry distillation of gallic acid. It forms colourless, odourless crystals, is readily soluble in water, alcohol and ether and its alkaline solution readily absorbs oxygen. It is used as a developer in photography.
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PYROLIGNEOUS ACID

Pyroligneous Acid (Essence of Smoke) is an impure acetic acid obtained by the distillation of wood. It is used for providing a 'smoked' flavour to bacon and dried fish.
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PYROMETER

A pyrometer is a device for measuring temperatures outside of the range of a mercurial thermometer. Wedgwood's pyrometer, the first which came into extensive use, was used by him for testing the heat of his pottery and porcelain kilns, and depended on the property of clay to contract on exposure to heat. Many different modes have been proposed or actually employed for measuring high temperatures; as by contraction, as in Wedgwood's; by the expansion of bars of different metals; by change of pressure in confined gases; by the amount of heat imparted to a cold mass; by the fusing-point of solids; by colour, as red and white heat, etc.
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PYROPHORUS

Pyrophorus is a name applied to certain substances or mixtures which take fire when exposed to the air, owing to the rapidity with which they combine with oxygen.
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PYROSCOPE

A pyroscope is an instrument for measuring the intensity of heat radiating from a hot body, or the frigorific influence of a cold body.
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PYROTECHNY

Pyrotechny is the science of making and using artificial fireworks, the chief ingredients of which are potassium nitrate, sulphur, and charcoal. Iron filings yield bright red and white sparks. Steel filings and cast-iron borings contain carbon, and give a more brilliant fire with wavy radiations. Copper filings give flame a greenish tint, those of zinc a fine blue colour; the sulphuret of antimony gives a less greenish blue than zinc, but with much smoke; amber, resin, and common salt give a yellow fire. Lampblack produces a very red colour with gunpowder, and a pink with nitre in excess. Verdigris imparts a pale green, copper sulphate and sal-ammoniac a palm-tree green. Lycopodium, formerlt also used in the manufacture of stage-lightning, burns with a rose colour and a magnificent flame.
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PYROXYLIC

Pyroxylic or wood spirit is the crude spirit obtained by distilling the volatile product of the dry distillation of wood, from which the tar has been separated and the acetic acid neutralized by lime. It consists chiefly of methyl alcohol and acetone, along with a number of other compounds, and is a brownish inflammable liquid. It is used as a solvent for making varnishes and also to mix with ordinary alcohol to denature it.
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PYROXYLIN

Pyroxylin is an alternative name for nitro-cellulose. The term pyroxylin is usually applied to the more soluble types of nitro-cellulose.
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PYRUVIC ACID

Pyruvic acid (2-oxopropanoic acid) is a colourless liquid organic acid with the formula CH3COCOOH. It is an important intermediate compound in metabolism, being produced during glycolysis and converted to acetyl coenzyme A, required for the Krebs cycle.
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PYTHAGOREAN THEOREM

Pythagorean Theorem (Pythagoras Theorey) is the forty-seventh proposition of the first book of Euclid's Elements, which shows that in any right-angled triangle the square of the hypotenuse is equal to the sum of the squares of the other two sides.
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