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The Probert Encyclopaedia of Science & Technology

T-1

In North America, T-1 is a digital carrier for a DS1-formatted signal.
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T-3

In North America, T-3 a digital carrier for a DS3-formatted signal.
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TACHOGRAPH

A tachograph is a device fitted to a motor vehicle which records its speed and distances travelled.
Tachographs are often called the spy in the cab by lorry drivers who are restricted in how long they may drive for by law.
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TACHOMETER

A tachometer is a device for measuring the velocity of machines or the rate of flow of liquids. The term was first used to describe a device used for measuring the velocity of running water in a river or canal, and which consisted of a wheel with inclined vanes, which were turned by the current. The rotations of the wheel were then recorded by clockwork.
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TACHYON

A tachyon is a theoretical particle that always travel faster than light.
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TACK

A tack is a small sharp nail, usually with a large flat head. They are used for fitting a light or thin object to a more solid one, such as carpet to the floor.
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TAIN

Tain is a form of thin tin plate or foil used for making mirrors.
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TALLOW

Tallow is the harder and less fusible fats of animals, especially sheep and ox, separated from the connective tissue by melting and clarifying and used for making soap, candles and other things. It is composed of the glycerol esters of stearic and oleic, as well as some palmitic acids.
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TAN

Tan is the bark of oak, birch, beech and other trees, shredded and steeped in water (the liquor being known as tan ooze) and used for the preparation of leather.
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TANG

A tang is a projection of a knife or other metal tool by which it is secured to its handle.
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TANGENT

In geometry, a rangent is a straight line which touches or meets a circle or curve in one point, and which being produced does not cut it; a straight line drawn at right angles to the diameter of a circle, from the extremity of it which being continued would merely touch and not cut the circle. In trigonometry the tangent of an arc is a straight line touching the circle of which the arc is a part, at one extremity of the arc, and meeting the diameter passing through the other extremity. The arc and its tangent have always a certain relation to each other; and when the one is given in parts of the radius, the other can always be computed. For trigonometrical purposes tangents for every arc from 0 degrees to 90 degrees, as well as sines, cosines, etc, have been calculated with reference to a radius of a certain length, and these or their logarithms formed into tables. In the higher geometry the word tangent is not limited to straight lines, but is also applied to curves in contact with other curves, and also to surfaces.
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TANGHININ

Tanghinin is a poison acting on the heart. It is obtained from the almonds of Tanghinia veneifera and is used in Madagascar for trial by ordeal.
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TANNER

Tanner is an old English slang expression for a sixpence. More properly, a
tanner is someone who tans hides.
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TANNERY

A tannery is a place where hides are tanned.
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TANNIC ACID

Tannic acid (tannin) is a peculiar acid which exists in every part of all species of oaks, especially in the bark, but is found in greatest quantity in gall-nuts. Tannic acid, when pure, is nearly white, and not at all crystalline. It is very soluble in water, and has a most astringent taste, without bitterness. It derives its name from its property of combining with the skins of animals and converting them into leather, or tanning them. It is the active principle in almost all astringent vegetables, and is used in medicine in preference to mineral astringents, because it is free from irritant and poisonous action. The name is generally applied to a mixture of several substances.
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TANNIN

Tannin is an alternative name for tannic acid.
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TANNING

Tanning is the operation of converting the raw hides and skins of animals into leather by effecting a chemical combination between the gelatine of which they principally consist and the astringent vegetable principle called tannic acid or tannin.

The object of the tanning process is to produce such a chemical change in skins as may render them unalterable by those agents which tend to decompose them in their natural state (preserve them), and in connection with the subsequent operations of currying or dressing to bring them into a state of pliability and impermeability to water which may adapt them for the many useful purposes to which leather is applied.

The larger and heavier skins subjected to the tanning process, such as those of buffaloes, bulls, oxen, and cows, are technically called hides; while those of smaller animals, such as calves, sheep, and goats, are called skins.

In preparing the hides and skins for tanning they are first subjected to certain cleaning operations, after which the tanning proper begins. The various substances traditionally used for tanning are oak, fir, mimosa, and hemlock bark, sumach, myrobalans, divi-divi, valonia-nuts, cutch, kino, gambir, and oak-galls - all of which contain tannic acid. The impregnation of the hides with this tannic acid. may be effected either by placing them between layers of bark (oak bark being the best) in a vat filled with water, or steeping them in a liquor containing a small at first, but steadily increasing proportion of tannic acid throughout a series of pits. This liquor usually consists of water in which the ground or crushed tanning material has been steeped. The raw hide takes about a year to prepare it for the best quality of leather.

There is also a process called tawning which is employed chiefly in the preparation of the skins of sheep, lambs, goats, and kids. In this process the skins are steeped in a bath of alum, salt, and other substances, and they are also sometimes soaked in fish-oil. The more delicate leathers are treated in this manner, those especially which are used for wash-leathers, kid gloves, etc.

After the leather is tanned it is finished for use by the process of currying. Various improvements have been attempted to be made in the art of tanning, such as the preparation of the skins by means of metallic solutions instead of by vegetable tan-liquor; the forced absorption of the tan by applying pressure between cylinders; and the preparation of the skins by a chemical agent, so as to induce a quicker absorption of the tan. It has been found, however, that the slow process followed by the old tanners produces leather far superior to that produced by the new and more rapid methods, though a fair leather for certain purposes may be produced in five to ten weeks.
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TANTALUM

Tantalum is a rare silvery-looking metal element with the symbol Ta. It is found chiefly in tantalite and obtained by reducing to potassium flouro-tantalate by means of sodium followed by fusion in vacuo. Tantalum is used as a wire in electric lamps. Tantalum was discovered by A G Ekeberg in 1802, but the metal was not isolated until 1905. Combined with carbon, tantalum becomes almost as hard as diamond, and has been used to increase the hardness and tensile strength of steel. Tantalum is unaffected by most acids.
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TANTALUS CUP

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A Tantalus cup is a philosophical toy, consisting of a siphon so adapted to a cup that, the short leg being in the cup, the long leg may go down through the bottom of it. The siphon is concealed within the figure of a man, whose chin is on a level with the bend of the siphon. Hence, as soon as the water rises up to the chin of the image, it begins to subside, so that the figure, Like Tantalus in mythology, is unable to quench its thirst.
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TAP-BOLT

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A tap-bolt is a threaded bolt which screws into a part, as distinct from a standard bolt which receives a nut.
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TAPPET

In engineering, a tappet is a projection within a moving shaft which strikes some other moving piece periodically. In motor car construction the term tappet is applied to a short shaft between the foot of a valve and a cam on the camshaft operating a valve.
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TAR

Tar is a black, oily liquid with a characteristic odour obtained by the distillation of coal, wood and bituminous minerals. Tar varies in composition according to its source, but all kinds consist largely of hydrocarbons and contain suspended carbon, to which the black colour is due. By subjecting tar to distillation various constituents are separated and are employed as the raw material for making aniline dyes. The solid and brittle mass left after distillation is known as pitch. Tar has been used medicine in the treatment of skin diseases since at least the start of the 20th century.

In computing, tar is the name of the Unix tape archiver program. Files compressed with tar are recognisable by the extension '.tar' or '.tgz'. The contents of the archive may be extracted in various ways. If the archive file has the extension .tar, then the command line 'tar -xvf filename.tar' will work. If the file has the extension '.tgz' or '.tar.gz' then it has also been 'zipped' and the command 'tar -xzvf filename.tar.gz' or 'tar -xzvf filename.tgz' will extract the contents. The contents of an archive may be listed by replacing the parameter letter 'x' with 't' such as 'tar -tvf filename.tar'.
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TAR BLACK

Tar black is a cheap coal-tar product used for such purposes as treating wooden posts which are to be in contact with the soil.
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TARAXACIN

Taraxacin is a bitter crystallizable principle contained in the milky juice of the dandelion (Leontodon Taraxacum), especially in the juice of the roots. It possesses tonic, aperient, and diuretic properties.
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TARTAR

Tartar, also known as argal or argol, (potassium tartrate) is a white crust deposited in wine casks during fermentation. The purified crystals are used in cooking, and often called cream of tartar. The term is also used for the concretion deposited upon teeth from saliva and comprised of phosphate of lime.
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TARTARIC ACID

Tartaric Acid is a popular name for dihydroxysuccinic acid. It occurs in many plants, particularly in the grape and is easily obtained from tartar.
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TARTRATE

Tartrate is a salt of tartaric acid. Some of the tartrates are of considerable importance, such as tartar emetic and Rochelle salts.
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TAWING

Tawing is the manufacture of sheep, lamb, and goat skins into white leather (a form of tanning).
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TAXIDERMY

Taxidermy is the art of preparing and mounting the skins of animals in a lifelike manner. In colloquial terms, stuffing dead animals.
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TDB

TDB by Netko, is a small, powerful free computer database program for the Windows operating system. With a little bit programming you can make very useful databases with many intelligent reports. The databases and reports are displayed in a tabbed window. With one right-click in a database you can simply maintain the data (edit, add, search, replace and delete records). Clicking on the header buttons allows you sort to data in the required order. Through the menu commands or toolbar you can open, save, import, export or print records or reports. There is a facility provided to generate graph's and display data with attractive shapes. Some statistics functions are also included. There are intelligent commands for reports, multiple field search and replace, extensive ASCII import/export function, integrity self-check to ensure you got the original, uninfected copy of the program and help file.
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TECHNETIUM

Technetium is an artificial element with the symbol Tc.
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TECHNOLOGY

Technology is the science or systematic knowledge of the industrial arts. Originally industrial arts were enumerated as spinning, weaving, dyeing, metallurgy, brewing, and the like.
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TECTONICS

Tectonics is the study of rock movements.
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TEDDER

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A tedder is a machine for spreading hay, consisting of a number of pitchforks attached to cranks on two large wheels and drawn by a tractor or horses etc.
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TEFLON

Teflon is a trade name for the polymer polytetrafluorethylene. It is widely used as a non-stick coating in cookware.
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TELAUTOGRAPH

The telautograph was a form of telegraph (the originator of the modern fax machine) whereby a message or drawing produced at the transmitter was instantly reproduced at the distant receiver. The Telautograph was invented by Elisha Gray and was later greatly improved around 1900 and required only two line wires. Sketches, etc, could be produced at the other end of the two lines. By the action of a set of small levers the pen at the receiving end followed exactly the movements of the pen at the sending end, rising from the paper when the sending pen was lifted, and dipped into the ink when the sending pen was so dipped.
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TELCAN

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Telcan was a system for recording and playing back vision and sound using reel-to-reel standard quarter inch magnetic tape. Telcan was developed by Michael Turner and Norman Rutherford in 1963, and allowed viewers to record television programmes and play them back for viewing at a later date .
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TELEGONY

Telegony is the theory of pre-paternal influence on offspring. That is, that a previous male mate may pass characteristics to an offspring conceived by the same mother, but a different father. No evidence has been furnished to support the theory, but never the less, it was a popular belief amongst animal breeders.
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TELEGRAPH

Telegraph is a general name for any instrument or apparatus for rapidly conveying intelligence beyond the limits of distance at which the voice is audible. Thus the word covers (1) the apparatus on the bridge and in the engine-room of ships for giving instructions regarding speed and direction of the engines; (2) flag-signalling used by the army and navy; (3) heliograph used by the army; (4) semaphore used by the navy on ships and at coast stations; (5) the electric telegraph. It was to a kind of semaphore apparatus that the name was first given.

In the ship telegraph there are two dials exactly similar, one on the bridge, the other in the engine-room. They are so connected that when the handle of the instrument on the bridge is placed at a particular order, the pointer in the engine-room points to the same order, and in its movement to that position it sounds a gong to attract the engineer's attention.

One mode of flag-signalling requires two flags, and employs the semaphore alphabet code, in which each letter is represented by a definite fixed position of the flags; in the other mode, one flag is used, and given short or long movements to correspond with the dots and dashes of the Morse code. The semaphore consists of two long arms mounted on pivots at the top of a pole; each arm is connected with a handle near the base, and the two follow exactly the movements of their respective handles. By varying the positions of the arms a complete alphabet is obtained. In the heliograph the sun's rays are utilized for signalling by reflection from a mirror.

The electric telegraph is what was ordinarily understood by the word telegraph. It was of many types, but most of them were based on the property possessed by soft iron of being rapidly magnetized or demagnetised by the influence of the electric current. This magnetization was utilized to move certain levers by which the transmitted signals could be translated into the letters of the alphabet. The chief parts were: (a) a source of electricity, (b) a conductor or line wire, (c) the transmitting apparatus, and (d) the receiving apparatus.

The source of electricity could be a number of primary cells, such as those used for ringing electric bells; or a number of secondary cells, such as those used for driving motors or for electric lighting; or it could be a small magneto-electric machine or a dynamo. The line wire could be of galvanized iron, or copper, suspended on insulators mounted on poles; or it could be a continuously insulated wire, i.e. surrounded for the whole of its length with a nonconducting covering, such as gutta-percha, India-rubber, or paper, the latter being protected from moisture by being hermetically sealed in a lead pipe. For protection from mechanical injury, underground wires were drawn into iron pipes or earthenware ducts.

The needle telegraph was one of the earliest instruments. Its transmitting portion consisted of a single lever in some cases, and of a double lever in others, by which a current could be sent to the line and through the apparatus at the other end, in either direction at will, or when the levers are at rest the instrument was in a condition to receive currents from line. The receiving portion consisted of a bobbin of fine insulated wire surrounding a small strip of soft iron kept permanently magnetized by a steel magnet. The soft-iron strip was fixed to a light spindle which passed through the dial of the instrument and carried a blackened light brass pointer or needle whose movement was limited by two ivory pins at the upper end. The action of an incoming current was to deflect the soft iron, and with it the needle, either to the right or to the left, in accordance with the direction of the incoming current. The combinations of these movements were utilized to form letters in accordance with the Morse code, a movement to the left representing a dot, and to the right a dash.

The Wheatstone ABC instrument was a magneto-electric telegraph, the current being generated by the turning of a handle. This current was first in one direction, then in the other, and only passed out to line when the pointer of the transmitting portion was moving. The pointer was stopped at any desired letter of the alphabet on the sending dial by the depression of the corresponding key. The receiving portion consisted of another and very much lighter pointer which was rotated by a ratchet actuated by the incoming currents, which moved it first in one direction, then in the other. The receiving dial had a set of letters in exactly the same order as those on the sending dial, so that, provided both pointers were started from the zero position, marked by a cross, the two pointers would always point to the same letters, and when the sending pointer was stopped at a particular letter, the receiving pointer also indicated that letter.

The Morse telegraph gave short and long signals which were transmitted by the depression of a lever, thereby connecting one pole of a battery to line, the other pole being connected to earth. The incoming currents passed through an electro-magnet, giving its armature a corresponding movement to that of the lever at the sending end. The other end of the armature raised or lowered a revolving inking disc which, when the armature was depressed, imprinted an ink mark on a moving paper band. The transmitted signals were thus recorded. The Morse sounder is practically the electrical portion of a Morse receiver. After some practice, one can learn to distinguish by the clicks of the lever whether the signals are short or long, and eventually to read Morse signals by sound.

The Wheatstone automatic or high-speed telegraph was a greatly improved Morse. The transmitting portion was very light, and was driven by gearing at a very high speed. The movement of the transmitting lever was controlled by a perforated paper tape whose holes corresponded to Morse signals, a dot being represented by two holes in line with a central hole, whilst a dash was represented by two holes set obliquely. The receiver was a greatly improved Morse receiver, the signals being received in dots and dashes on the ordinary Morse paper band. The speed achieved with the Wheatstone automatic telegraph was 500 words a minute.

The Hughes instrument was a printing telegraph, recording the received signals in Roman type on a paper band. It had twenty-eight keys similar to those of a piano, representing the letters of the alphabet, and two spacing keys. These keys controlled the type-wheel at the sending end, and at the same time could transmit currents to line. These currents in passing through an electro-magnet at the receiving end released certain levers, which caused a paper band to be lifted against the type-wheel at the correct moment to print the corresponding letter of the key that was depressed at the sending end. The Baudot telegraph was also a printing system, in which different combinations of five keys were used to represent the letters of the alphabet. The great utility of this system was that one line wire was used for the transmission of as many as eight messages at practically the same instant. It was one of what are known as the multiplex systems, and was largely mechanical.

The syphon recorder was used for working on long cables. The signals were transmitted by two levers on the same principle as the needle telegraph. The received currents passed through a suspended coil, to which a very light glass tube known as the syphon was attached. At one end it dipped into an ink-well, whilst its other end just cleared a paper band. When once the ink was properly through the syphon, the movement of the paper drew out the ink, whilst a further supply was drawn in at the other end. The signals were thus recorded in a wavy, unbroken line, and the movements to the right or left of the centre represented the dots and dashes of the Morse code.

As early as 1747 Bishop Watson showed that signals might be sent through a wire stretched across the Thames by discharging a Leyden-jar through it. Lesage in 1774 erected at Geneva a telegraph line consisting of twenty-four wires connected with the same number of pith-ball electroscopes, each representing a letter. Volta's discovery of the galvanic pile and Oersted's discovery of electro-magnetism afforded much greater facilities for transmitting signals to a distance. Ampere, in 1820, proposed to utilize Oersted's discovery by employing twenty-four needles to be deflected by currents sent through the same number of wires; and Baron Schilling exhibited in Russia, in 1832, a telegraph model in which the signals appear to have been given by the deflections of a single needle. Weber and Gauss carried out this plan in 1833 by leading two wires from the observatory of Gottingen to the Physical Cabinet, a distance of about 9000 feet. The signals consisted in small deflections of a bar-magnet suspended horizontally with a mirror attached, on the plan since adopted in Thomson's mirror galvanometer. At their request the subject was earnestly taken up by Professor Steinheil of Munich, whose inventions contributed more perhaps than those of any other single individual to render electric telegraphs commercially practicable. He was the first to ascertain that earth connections might be made to supersede the use of a return wire. He also invented a convenient telegraphic alphabet, in which, as in most of the codes since employed, the different letters of the alphabet were represented by different combinations of two elementary signals. His currents were magneto-electric, like those of Weber and Gauss. The attraction of a movable armature by an electro-magnet furnishes the means of signalling which was the foundation of Morse's telegraphic system.

About the year 1837 electric telegraphs were first established as commercial speculations in three different countries. Steinheil's system was carried out at Munich, Morse's in America, and Wheatstone and Cooke's in England. The first telegraphs ever constructed for commercial use were laid down by Wheatstone and Cooke on the Great Western and London and Birmingham Railways. The wires, which were buried in the earth, were five in number, each acting on a separate needle. The single-needle and double-needle telegraphs of the same inventors were more extensively used. In 1872 a method of sending simultaneously two messages in opposite directions on the same wire was introduced (duplex telegraphy), and it was also discovered that two-messages could be sent in the same direction (diplex telegraphy), The two plans being combined, formed the quadruples system.

The telegraph was first brought into practical use in the United States by Professor Samuel Morse. He began his experiments in 1832, aided by L D Gale and George and Alfred Vail. In 1837 he filed a caveat in the Patent Office at Washington, and in 1840 obtained a patent covering the improvements he had made in the meantime. The first line established was between Baltimore and Washington, it being successfully operated on May the 27th, 1844.

In October, 1842, Morse had attempted to operate a line from Governor's Island to the Battery in New York, but this experiment failed. Samuel Colt, in 1843, laid a submarine cable from Coney Island and Fire Island, at the mouth of New York harbour, up to the city, and operated it successfully for a time. In 1860 it was estimated that there were over 50,000 miles of telegraph lines in operation in the United States, and at the end of the 19th century the lines extended over 190,000 miles.

Wireless telegraphy in its practical applications came into existence since 1888, when Hertz demonstrated the existence in the ether of the so-called 'Hertzian waves', produced by an oscillatory electric spark, and spreading out in all directions. Such wave-movements produced at the transmitting station and radiated through space can be detected at a distance, provided a sufficiently sensitive receiver or 'wave-detector' is employed. The receiving stations are provided with an aerial wire or wires in which the electric waves set up oscillations, which in turn affect an extremely delicate piece of apparatus known as a coherer. In early practical wireless telegraphy, series of waves were transmitted on the Morse system, and were received on a Morse receiver, or were read as from a sounder by means of a telephone receiver. In connection with wireless telegraphy the name of Marconi is the most familiar.
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TELEGRAPHONE

The telegraphone was a form of telephone apparatus invented by Valdemar Poulsen, a Dane, which received the fluctuations of current produced by sound waves on the transmitter, and transformed them into magnetic fluctuations, which were stored up for any length of time, and could be converted back again into sound-waves at will. Its essential part consisted of two drums of fine steel wire and a small electromagnet. While the wire was unwinding from one drum and winding on to the other, it passed close to the poles of the electromagnet, and the variations of current in the electro-magnet were recorded on the wire as a series of magnetic fluctuations due to varying magnetization. This magnetic writing, as was called, could be reproduced in the form of sound by winding back the wire to its initial position and then unwinding it as before past the same electro-magnet, then connected to an ordinary telephone receiver. Another form of the instrument gave disc records, which could be reproduced on a similar instrument.
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TELEGRAPHY

Originally the term telegraphy referred to any form of signalling. With the advent of electronic telegraph systems the term became more specific to electronic signalling, and more recently to the transmission of data, as distinct from telephony which signals voice, electronically. E.G.: Morse code by radio wave or through a telephone line.

The early electric telegraph system in use in the USA during the 1890s used a four wire system capable of simultaneously transmitting four messages (known as telegrams). International telegraphic messages were sent via relay points, for example, in 1892 a message sent from San Francisco in the USA to Hong Kong took about 15 minutes to arrive and the message went via New York, Canso, Penzance, Aden, Bombay, Madras, Penang and Singapore.
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TELEMETER

A telemeter was an instrument for measuring the distance of an object from the observer. Telemeters were used in surveying and by the military during the 19th and early 20th centuries. Later telemeters consisted of a rigid tube, mounted so that it could pivot horizontally and vertically. At each end of the tube and at right angles to its main axis was a telescope, the images being deflected by prisms to an eyepiece at the centre of the tube. One prism was fixed to maintain the beam of light at a right angle and the other prism was adjusted either by turning on its axis or sliding along the tube, until the images from the two telescopes coincided. At this point the range of the object being viewed could be read off on a graduated scale.
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TELEMETRY

Telemetry is one-way radio transmissions used for tracking and measurement data.
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TELEONOMY

Teleonomy is the property of living systems of being organized towards the attainment of ends without true purpose
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TELEPHONE

The telephone is an instrument for reproducing speech at a distance from the source. It was invented (or rather patented) by Alexander Graham Bell in 1876 - the invention of the telephone being claimed also by Gray, of Chicago and several others. The possibility of such an instrument was discovered previous to 1873, but the first satisfactory results were not obtained until 1877, when Alexander Graham Bell completed and put into practical use a telephone line between Salem and Boston, Gray achieving a like result the same year in a line set up between Chicago and Milwaukee, a distance of eighty-five miles. By 1880 there were in existence in America 148 telephone companies and private concerns, operating 34,305 miles of wire which by 1893 had risen to 308,000 miles. The Bell Company was the most extensive American telephone company in the 19th century. Two suits were brought against the patent, but both failed.

Early telephone systems had a limited range, in 1892 the longest distance at which telephone conversations were regularly maintained was 750 miles which took place between Portland in Maine and Buffalo in New York in the USA. Long distance telephony was developed in the 1920s following the experiments of Dr H. W. Nichols, with links between major cities in the continents introduced in 1927.
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TELEPHONY

Telephony refers to the reproduction of speech at a distance from the source. Telephony may occur with the use of a telephone, or through wireless apparatus such as radio equipment.
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TELESCOPE

A telescope is an optical instrument essentially consisting of a set of lenses fixed in a tube or a number of sliding tubes, by which distant objects are brought within the range of distinct, or more distinct vision. The law of action by which the telescope assists human vision is twofold, and that under all the varieties of its construction. A distant object viewed by the unaided eye is placed in the circumference of a large circle, having the eye for its centre, and consequently the angle under which it is seen is measured by the minute portion of the circumference which it occupies. Now, when the distance is great, it is found that this angle is too small to convey to the retina any sensible impression - all the light proceeding from the object is too weak to affect the optic nerve. This limit to distinct vision results from the small aperture or pupil of the eye. The telescope substitutes its large object lens or reflector for the human eye, and consequently receives a quantity of light proportioned to its area or surface; hence a distant point, inappreciable by the eye alone, is rendered visible by the aid of the telescope. The rays of light, after transmission or reflection, converge to a point as they at first proceeded from a point, and thus an image of the object is formed which, when viewed by the eye-piece or lens, is more or less magnified. The telescope therefore assists the eye in these two ways: it gathers up additional light, and it magnifies the object; that is to say, its image.

The refracting telescope is constructed of lenses alone, which, by successive refractions, produce the desired effect. This instrument was formerly very cumbersome and inconvenient, in as much as its length had to be increased considerably with every accession of power; but the substitution of achromatic for ordinary lenses rendered it more portable and convenient.

The reflecting telescope is composed of specula or concave reflectors aided by a refracting eye-piece. To this instrument we owe some of the most wondrous discoveries in astronomical science. The names of Newton, Gregory, Herschel, and Lord Rosse are connected with its history.

The refracting telescope in its simplest form comprises two lenses of different focal lengths. Rays of light from a distant object falling upon the first object-glass are converged to a focus at some distance beyond the first lens. The second lens, or eye-glass is placed at its focal distance from the point of convergence, gathers up the diverging rays and carries them parallel to the eye, magnifying the image formed by the first lens. The magnifying power of the instrument is as the focal length of one lens to that of the other. In this construction the object is seen inverted or turned upside down, and hence it is unsuitable for terrestrial purposes. To render the image erect, and thus show it in its natural position, a more complicated eye-piece, consisting of two additional lenses, is necessary.

Another refracting telescope, consisting of two lenses in its simplest form, is called the Galilean telescope. It differs from the former in having a concave lens for its eye-glass, which lens is placed nearer the object-glass than the focus of this lens, producing an image which is not inverted. This kind of telescope is the one used in opera-glasses and field-glasses.
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TELESCOPE JOINT

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A telescope joint is an electrical end to end joint used for joining large multi-strand cables where the diameter of the joint must not exceed that of the cable. It is a fairly efficient joint, but will not withstand bending or strain. The outer half of the conductors are cut away from one cable, the inner half of the other cable, before the ends are filled square, and the two cables set together, the ends held with a few turns of binding wire and the joint is soldered. After cooling the binding wire is filled smooth.
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TELETEXT

Teletext is a television-based information system. Teletext is a videotex service, transmitting information in the unused area (usually the top four lines) of a normal television signal. By using a special decoder attached to the television set, this information becomes visible on the entire screen as pages of text and graphics.
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TELEVISION

Television is a system for seeing distant objects through the intermediary of electro-magnetic waves transmitted through space or over wires. It was first developed during the 1920s.
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TELEX

Telex is an international communications network designed on a similar basis to the telephone network, to carry telegraphic messages between teleprinters. For simple messages
telex has the advantage over fax that one telex message can be transmitted to several receivers simultaneously. In 1985 an improved telex system was launched, which can use any public communications network, and is faster and cheaper.
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TELLURION GLOBE

The Tellurion Globe was a scientific instrument invented by Naish, of Brighton, of St John's College, Cambridge. The Tellurion Globe was designed to show the diurnal and annual motions of the earth and its positions with regard to the sun. It was exhibited at a late meeting of the Royal Institution, and again at the soires of the Royal Geographical Society, in mid-1866, where it was much approved. Machines for similar purposes had often been constructed to aid the popular teaching of astronomy, but had been found liable to some objections; first, on account of the impossibility of arranging globes in size and distance proportionate to the magnitude of the solar system; and, secondly, because of the difficulty of producing orbital motions having the same exact variation as those of our planet. By this machine it was considered both those objections were now completely removed, as neither the globe of the sun nor the sun's distance from the earth was apparent, and the true orbital motion was obtained by an arrangement of the utmost simplicity. The daily and yearly changes produced by the sun's light at any point of the earth's surface depend on its angular position with regard to the sun's centre. This position, again, depends, not on the sun's magnitude, or on the earth's distance from the sun, but on the motions of the earth upon its axis and in its orbit, together with the inclination of the axis to the plane of the orbit. In this machine, therefore, the sun and its distance are reduced each to a minimum, and the space thus saved is appropriated to the enlargement of the terrestrial body. False conceptions of magnitude are thus prevented, for the sun becomes a point, and its position is always near the earth's surface. Moreover, in consequence of the augmented size of the globe representing the earth, the smallest motion, either on its axis or in its orbit, becomes very conspicuous; and if the orbital motion be a perfect imitation of that of the earth in space,
he whole theory of terrestrial astronomy, in cause and effect, will be correctly exhibited.

The variable motion in the orbit was determined by the following considerations. 'Of the two focal points in an elliptic orbit, one is the sun's centre; the other is unoccupied. If the focal points be near each other, as in the earth's orbit, this peculiar result takes place : A body moving in the curve round the unoccupied focus, and with uniform motion, will at the same time as moving round the other focus, or sun's centre, with true variable motion. The earth's motion upon its axis is also uniform; therefore, since the earth's motion upon its axis, and its orbital motion about the non-solar focus, are both of the same kind - that is, uniform - they can be imitated mechanically by direct communication, so that the result will be, if the focal points be properly adjusted, a perfect imitation of the earth's motion in space round the sun.' The adaptation of circles to measure the various motions was an affair of mere detail; these were all graduated, and the very few wheels required were concealed from view.

The Tellurion Globe was mounted in a circle, similar to the common brass meridian one of like uses. This circle was supported on a vertical Spindle which, passing through a revolving horizontal shield, communicated with wheels below, and preserved a constant direction of the earth's poles. The circle referred to is thus a sidereal day-circle, and a solstitial colure; its vertical diameter is the axis of the ecliptic, and a revolution, when required, about this diameter, exhibited the precession of the equinoxes. Through the centre of the revolving shield rose a vertical spindle to the level of the globe's centre, when it became the non-solar focus, and supported the line of apsides, which contained the solar focus, or sun's centre, adjustable by a screw, and showed apogee and perigee. Inclosing the sidereal day-circle was another, determining the ever-changing boundary of sunlight on the earth and defining day and night at any time and place. It was kept symmetrical with the sun-focus by an index, which, passing through the latter, showed the sun's true longitude on any day.

Passing through the other focus was an index showing the sun's mean place. The angle between these indices, at any time, was denoted by a graduated arc, and became an important element in the equation of time. The sun's vertical position over any point of the earth was shown by a small index directed from the solar focus, and defined altitude, declination, or amplitude. The above true and mean longitudes of the sun were pointed out upon a horizontal circle, having the solar focus for its centre, and inscribed, like the horizon of the common globe, of which it was almost an exact copy; but the constellations and signs of the Zodiac were distinguished from each other to show the effect of precession. There was a six o'clock meridian-circle, upon which the hour circle, like a ring, was mounted at the equator; and upon this latter another ring, adjustable to become the horizon of any place on the earth. The result was that the sun's position in respect to any place was measured with great accuracy, and the phenomena depending thereon were represented in minute detail.

The diurnal and annual motions were given separately and in combination, so that the effect of each could be estimated and the globe placed at once in any assigned point of its orbit. This being effected and the horizon adjusted, there was presented to the eye a full and exact epitome of simultaneous conditions corresponding to the given time and place. For example, let it be required to find at what hour the sun rises at London on a given day. Having elevated the horizon and given the necessary orbital motion, not only was the correct hour shown, but the point of the horizon at which the sun rises, the length of the day, the sun's true longitude, right ascension and declination, that place on the earth over which the sun is vertical, and all places which then have noon, midnight, sunrise or sunset, were indicated respectively, together with the equation of time. But any one of these particulars might have been the original object of inquiry, when all the others would have been exhibited in joint dependence and definitely determined. A motion of the globe on its axis would reveal numerous other details for the given day. Since the horizon can be made coincident with any plane passing through the earth's centre, and is a great circle of the globe, it served all the uses of the quadrant of altitude.
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TELLURIUM

Tellurium is a greyish-white semi-metallic element with a metallic lustre and the symbol Te. A semiconductor, it shows greater conductivity in certain directions, according to the alignment of the atoms. Tellurium is found in small quantities in its native state, but usually combined with metals such as tetradymite or bismuth telluride. Tellurium was named by Klaproth who examined it in 1798. Its compounds are toxic. The chief use of tellurium is in the vulcanisation of rubber. It is also used to colour glass, to increase the hardness of lead in battery plates, and to improve the machinability of stainless steel.
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TELPHERAGE

Telpherage is a system of traction by aerial ropeway used for the conveyance of minerals over rough country. A stout steel cable supported on poles forms the track and on this are hung small trolleys with wheels running on the cable. A second cable conveys electric current to the trolleys which are driven by motors, each trolley being equipped with its own self-propelling motor. Telpherage was devised by Professor Fleeming Jenkin in 1881 and the system was developed in conjunction with Professors Ayrton and Perry.
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TEMPERA

Tempera is a process of spreading a mixture of paint and a glutinous material on a flat surface. It is a process which was popular with early Italian artists.
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TEMPERATURE

The temperature of a substance is a number which expresses its degree of hotness on some chosen scale. It does not relate to the heat energy contained by the object.
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TEMPERING

Tempering is the process of heating up a metal, such as steel until red hot and then suddenly or gradually cooling it in water, oil, molten lead or another liquid. The result is to harden the metal. The metal can then be gradually reheated to reduce the hardness down to a required level - very hard metal also being more brittle. Oil and lead tempering produce a metal which though less hard, is not so brittle as metal tempered by water hardening.
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TEMPEST

Tempest (Transient Electromagnetic Pulse Surveillance Technology) is the US Government program for evaluation and endorsement of electronic equipment that is safe from eavesdropping. Tempest certification refers to the equipment having passed a testing phase and agreeing to emanations rules specified in the government document NACSIM 5100A (Classified). This document sets forth the emanation levels that the US Government believes equipment can give off without compromising the information it is processing. Computers and other electronic equipment release interference to their surrounding environment. You may observe this by placing two video monitors close together. The pictures will behave erratically until you space them apart. What is important for an observer is the emission of digital pulses (1s and 0s) as these are used in computers. The channel for this radiation is in two arrangements, radiated emissions and conducted emissions. Radiated emissions are assembled when components in electrical devices form to act as antennas.

Conducted emissions are formed when radiation is conducted along cables and wires. Although most of the time these emissions are simply annoyances, they can sometimes be very helpful. If someone wants to see what project a person is working on they can sit in a van outside the target's office and use sensitive electronic equipment to attempt to pick up and decipher the radiated emissions from the target's video monitor. These emissions normally exist at around 55-245 Mhz and can be picked up as far as one kilometre away. A monitoring device can distinguish between different sources emitting radiation because the sources emanating the radiation are made up of dissimilar elements and so this coupled with other factors varies the emitted frequency. For example different electronic components in VDUs, different manufacturing processes involved in reproducing the VDUs, different line syncs, etc.
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TENON-SAW

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A tenon-saw is a fine saw with a thin blade and small teeth designed for cutting tenons.
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TENT MALLET

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A tent mallet is a crude large wooden hammer comprising a cylindrical wooden head fixed to a long wooden shaft and used for driving tent pegs into the ground.
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TERATOLOGY

Teratology is the science concerned with the study of occurrences of malformations, monstrosity or abnormal growths in organic life (monsters).
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TERBIUM

Terbium is a metal element with the symbol Tb belonging to the series known as rare earths.
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TEREBINE

Terebine is a very strong liquid drier made by dissolving drying agents such as lead or manganese salts in linseed oil at a high temperature, usually with the addition of rosin, and thinning down the mixture with white spirit.
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TERPENE

Terpene is a chemistry term for any of a large group of cyclic hydrocarbons which form the chief constituents of the volatile oils obtained by distilling plant material (Turpentine).
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TERPINEOL

Terpineol is a thick liquid produced by the action of dilute acids upon terpine hydrate. It has a smell resembling lilac or hyacinth and is used in perfume and soaps to imitate the smell of these flowers.
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TERRA COTTA

Terra Cotta is a baked clay, or burned earth material similar to that from which pottery is made. It was extensively used in ancient times. Terra Cotta consists of potters' clay and fine powdered silica.
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TETRA-ETHYL-LEAD

Tetra-Ethyl-Lead is an organo-metalic compound widely used as an anti-knock agent in leaded petrol.
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TETRACHLOROETHANE

1,1,2,2-Tetrachloroethane is a man-made colourless or pale yellow dense liquid with a penetrating, sweet chloroform-like odour. The only major use for it is as a feedstock in the production of trichloroethylene, tetrachloroethylene, and 1,2-dichloroethylene. It may also be used as a solvent; in cleaning and degreasing metals; in paint and rust removers, varnishes and lacquers; in photographic films; and as an extractant for oils and fats. It was once an ingredient in an insect repellent, but registration was cancelled in the late 1970s. Due to its toxicity and new processes for manufacturing chlorinated ethylenes, the manufacture and use of 1,1,2,2-tetrachloroethane now appears to be very limited. 1,1,2,2-Tetrachloroethane does not burn easily, but produces poisonous gases in a fire, including phosgene and hydrogen chloride. It is soluble in alcohol and ether. It is also known as acetylene tetrachloride; di-chloro-2,2-dichloroethane; s-tetrachloroethane; TCE
tetrachloroethane; and sym-tetrachloroethane.
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TETRAGON

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A tetragon (from the Greek tetra meaning four and gonia, meaning corner or angle) is a plane figure having four angles. Thus a square, a rectangle and a parallelogram are all forms of tetragon.
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TETRAHEDRON

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In geometry, a tetrahedron is one of the five regular solids. It is a figure comprehended under four equilateral and equal triangles, or a triangular pyramid having four equal and equilateral faces.
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TETRODE

A tetrode is an electronic amplifying valve with four main electrodes.
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TEX

TeX is an extremely powerful macro-based computer text formatter written by Donald E. Knuth, very popular in the computer-science community. Knuth began TeX because he had become annoyed at the declining quality of the typesetting in volumes I--III of his monumental `Art of Computer Programming'. In a manifestation of the typical hackish urge to solve the problem at hand once and for all, he began to design his own typesetting language. He thought he would finish it on his sabbatical in 1978; he was wrong by only about 8 years. The language was finally frozen around 1985. Though well-written, TeX is so large (and so full of cutting edge technique) that it is said to have unearthed at least one bug in every Pascal it has been compiled with.
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TEXTPAD

TextPad is a full-featured text editor offering a spelling checker, macros, and powerful formatting and file-storage options for the Windows operating system. Features include colour syntax highlighting, multiple workspaces, customisable toolbars, a dockable document selector, and an alternative tabbed-document selector.
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TEXTREADER

TextReader V1.1 is an auto-scrolling text reader computer program for the Windows operating system, allowing the user to read through large text and rich-text files (such as Project Gutenberg files) without having to page through the text. The user has the ability to set such features as the scroll rate, font characteristics for the reader and each file. The program also features a text search facility.
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THALLIUM

Thallium (named after the Greek thallos, meaning a green twig) is a metal element with the symbol Tl. Thallium was discovered by Crookes in 1861, in a deposit from a sulphuric acid manufactory in the Hartz. In its physical properties thallium resembles lead, but is slightly heavier, somewhat softer, and may be scratched by the finger-nail. It melts at 290 degrees centigrade, and is soluble in the ordinary mineral acids. In colour it resembles silver, but is less brilliantly white. Its specific gravity varies from 11.8 to 11.9, according to the mechanical treatment to which it has been subjected. The tenacity of the metal is less than that of lead; it is possessed of very considerable malleability. Thallium and its salts impart an intense green colour to a non-luninous flame; when a flame so coloured is examined by the spectroscope one very brilliant green band is noticed, somewhat more refrangible than the sodium line D. The salts of thallium are exceedingly poisonous. Thallium forms two oxides, giving rise to thallous and thallic salts. SmaIl quantities of thallium are widely distributed in nature, the metal frequently occurring in iron and copper pyrites, in native sulphur, etc.
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THE BROOKLYN BRIDGE

The Brooklyn Bridge was a hardware/software package that let the user link two PCs through their serial or parallel ports to perform file transfers and share DOS devices. Through a master/slave relationship, the two computers were completely integrated, and you could access the disk drives and other DOS devices of one computer from the other. The package allowed the transfer of files serially at speeds up to 115,200 bps, or up to 500,000 through the parallel ports.

The Brooklyn Bridge gave users the option of operating the program through DOS commands, Brooklyn Bridge utilities, or menus. The latter two methods included a context-sensitive help facility. Once installed, the software required only 5K of memory. The Brooklyn Bridge operated as a DOS device driver, transparently linking two computers to make the remote system's drives appear as the next available drive letters on the machine one was using. For example, a PC with two disk drives and one hard disk occupies drives A:, B:, and C:. The disk drives of a laptop PC are seen as D: and E:. A file was also included to rename the designators of the remote devices so as not to conflict with those of the local PC. For example, if one had LPT1 defined on both the local and remote PC, you could rename the remote LPT1 to LPT2, so both could be accessed from the local PC.

The Brooklyn Bridge was more than just a device for file transfers between two computers; it was a small network. The Brooklyn Bridge allowed the user to read and write to diskette drives and hard disks, and use printers, plotters, clock, calendar and other DOS devices connected to the remote PC.
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THE CONSERVATION OF ENERGY AND MASS

Early in the twentieth century Albert Einstein put forward new ideas regarding the relationship between space, time, mass and energy which have come to be known as the theory of relativity. It had long been accepted that matter could not be destroyed. This assumption was expressed in the law of conservation of matter, which states that the total quantity of matter in the universe is fixed and cannot be increased or decreased by human agency.

Similarly, another law, called the law of conservation of energy, states that the total quantity of energy in the universe is also constant and can be neither created nor destroyed. Einstein simplified the picture of the universe by showing that the mass of a body is a measure of the quantity of energy contained in it. For example, in a nuclear reactor, the sum total of the masses of the atoms produced as a result of fission is slightly less than the mass of the original uranium nuclei. The difference represents the mass of the energy liberated as heat, radiation and kinetic energy of fission products. Thus we now have to consider the laws of conservation of energy and mass as separate aspects of a single principle and take the view that the sum total of mass plus energy in the universe is fixed.
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THE ONION ROUTER

The Onion Router, or Tor, is an American volunteer-run computer network project that offers free software to those seeking anonymous online communication, like a more respectable version of Freenet. The Onion Router allows individuals to surf questionable websites and services without leaving tell-tale tracks.
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THE PRINCIPLE OF THE ELECTRIC MOTOR.

A motor is a device for converting electrical energy into mechanical energy. In its simplest form it consists of a rectangular coil which can turn about a horizontal axis. The coil is placed in the uniform field due to the poles of a permanent magnet, the axis being perpendicular to the direction of this field. By the rule for the magnetic effect of a current flowing round a coil, the sides of the coil act like poles of a magnet. If the current is so arranged initially that the sides of the coil are polarised the same as the sides of the magnet they are adjacent to, the coil will turn so that its north polarised side faces the south pole of the magnet. When the plane of the coil reaches the vertical position it overshoots and moves past, just as the mass at the end of a simple pendulum moves past its equilibrium position as it oscillates to and fro. As the coil passes this vertical position, the current in it is made to reverse by a split-ring commutator device and the formerly north pole face of the coil becomes a south pole. It is therefore repelled by the south pole of the magnet and attracted by the north pole, and thus the coil continues to rotate in the same direction about its axis. When it reaches a vertical position on its way round the current is again reversed by the commutator to make the rotation continue.
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THEBAINE

Thebaine is a naturally occurring non-addictive, non-narcotic alkaloid contained in opium. It is coloured red by concentrated sulphuric acid and is very poisonous, causing severe convulsions by its action on the spinal cord and generally resembling strychnine in its results. However, it can also be used to produce codeine and other pain killers, and is very difficult to derive morphine (from which opium is produced) from it.
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THEINE

Theine is an alternative name for caffeine, the term theine usually being given to a drug prepared from the dried leaves of certain plants.
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THEOBROMINE

Theobromine (dimethyl-xanthine) is the active principal of the cacao or cocoa bean. It is an alkaloid crystalline powder with a bitter taste closely resembling caffeine and sometimes used as a diuretic and has been found to be an effective cough suppressant, more effective than codeine - eating chocolate, particularly plain chocolate, or drinking cocoa can be an effective remedy for coughing.
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THEODOLITE

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A theodolite is an instrument used in surveying for measuring horizontal and vertical angles by means of a telescope the movements of which can be accurately marked. This instrument is variously constructed, but its main characteristics continue unaltered in all forms. Its chief features are the telescope, a graduated vertical circle to which it is attached, two concentric horizontal circular plates which turn freely on each other, and two spirit-levels on the upper plate to secure exact horizontality, the whole being on a tripod stand. The lower plate contains the divisions of the circle round its edge, and the upper or vernier plate has two vernier divisions diametrically opposite. The plates turn on a double vertical axis. To measure the angular distance horizontally between any two objects, the telescope is turned round along with the vernier circle until it is brought to bear exactly upon one of the objects; it is then. turned round until it is brought to bear on the other object, and the arc which the vernier has described on the graduated circle measures the angle required. By means of the double vertical axis the observation may be repeated any number of times in order to ensure accuracy. The graduated vertical circle is for taking altitudes or vertical angles in a similar way. The theodolite is a most essential instrument in surveying and in geodetical operations.
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THEORY OF PROJECTILES

The theory of projectiles is that branch of mechanics which deals with the motion of bodies thrown or driven some distance by an impelling force, and whose progress is affected by gravity and the resistance of the air. The most common cases are the balls projected from guns or other firearms. If thrown horizontally, the body will move in a curved path, because it retains unchanged (leaving out of account the resistance of the air) its horizontal velocity, while it falls faster and faster towards the ground. A body projected obliquely has initially a certain horizontal velocity and a certain vertical velocity. It retains its horizontal velocity unchanged, but its vertical velocity is altered by the force of gravity, and in both of these cases we find that the path of the projectile is a parabola. With a given velocity the greatest range of a projectile is obtained by projecting at an angle of 45 degrees with the vertical. The actual path of a bullet is always within the parabola of the theoretical projectile, and hence the range of a gun is much less than what the parabola would give. The range depends also upon the shape and weight of the projectile as well as upon its initial velocity.
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THERMION

A thermion is an electrically charged particle emitted from a heated body.
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THERMIONICS

Thermionics is a branch of physics dealing with the emission of ions by hot bodies. The first thermionic observation, though not understood at the time, was made by Thomas Edison, and is known as the Edison effect.
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THERMISTOR

A thermistor is a type of semi-conductor in which the resistance decreases as the temperature rises.
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THERMIT

Thermit is a mixture of coarsely powdered aluminium and magnetic oxide of iron which when ignited - by means of a primer of barium peroxide mixed with aluminium powder into which a piece of magnesium ribbon is placed and ignited - reacts by producing iron and aluminium oxide at an intensely high temperature approaching 3000 degrees Celsius. It was developed for making welding repairs to rails and welding in situ, and was adopted by the army for use in incendiary bombs. German incendiary bombs dropped on Britain during the Great War contained thermit.
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THERMITE PROCESS

The Thermite Process (Goldschmidt Process) is the method of obtaining liquid metal by reduction of the oxide with aluminium powder.
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THERMO-CHEMISTRY

Thermo-Chemistry is the branch of physical chemistry which deals with the relationship between chemical energy and heat.
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THERMO-ELECTRICITY

Thermo-Electricity is electricity produced at the junction of two metals, or at a point where a molecular change occurs in a bar of the same metal, when the junction or point is heated above or cooled below the general temperature of the conductor. Thus when wires or bars of metal of different kinds, as bismuth and antimony, are placed in close contact, end to end, and disposed so as to form a periphery or continuous circuit, and heat then applied to the ends or junctions of the bars, electric currents are produced. The thermo-electric battery, or pile, was an apparatus formerly much used in delicate experiments with radiant heat, and consisted of a series of little bars of antimony and bismuth (or any other two metals of different heat-conducting power), having their ends soldered together and arranged in a compact form; the opposite ends of the pile being connected with a galvanometer, which was very sensibly affected by the electric current induced in the system of bars when exposed to the slightest variations of temperature. To the combined arrangement of pile and galvanometer the name of thermo-multiplier was given. Two metal bars of different heat-conducting power having their ends soldered together, and the combined bar then usually bent into a more or less horse-shoe or magnet form for the purpose of bringing their free ends within a conveniently short distance, designated a thermo-electric pair, were much used in thermo-electric experiments. But as the electric current developed in a single pair is very weak, a considerable number were usually combined to form a thermo-electric pile or battery. Bismuth and antimony were the metals usually employed, the difference in electro-motive force being greater between them than between any other two metals conveniently obtainable.
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THERMODYNAMIC ENGINE

A thermodynamic engine is any form of heat engine (such as gas or steam engines for example) by means of which a percentage of the heat lost by one body called the source, on account of its connection with another body called the refrigerator, is converted into kinetic energy or mechanical effect, and made available for the performance of work. The efficiency of a heat engine is the ratio of the heat available for mechanical effect to the total heat taken from the source. A reversible engine is called a perfect engine, because it is the most efficient engine between the temperatures of its source and refrigerator.
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THERMODYNAMICS

Thermodynamics is the study of the laws that govern the conversion of energy from one form to another, the direction in which heat will flow, and the availability of energy to do work. It is based on the concept that in an isolated system anywhere in the universe there is a measurable quantity of energy called the internal energy (U) of the system. This is the total kinetic and potential energy of the atoms and molecules of the system of all kinds that can be transferred directly as heat; it therefore excludes chemical and nuclear energy. The value of U can only be changed if the system ceases to be isolated. In these circumstances U can change by the transfer of mass to or from the system, the transfer of heat (Q) to or from the system, or by the work (W) being done on or by the system. For an adiabatic (Q = 0) system of constant mass, DU = W. By convention, W is taken to be positive if work is done on the system and negative if work is done by the system. For nonadiabatic systems of constant mass, DU = Q + W. This statement, which is equivalent to the law of conservation of energy, is known as the first law of thermodynamics.

All natural processes conform to this law, but not all processes conforming to it can occur in nature. Most natural processes are irreversible, i.e. they will only proceed in one direction. The direction that a natural process can take is the subject of the second law of thermodynamics, which can be stated in a variety of ways. R Clausius stated the law in two ways: 'heat cannot be transferred from one body to a second body at a higher temperature without producing some other effect' and 'the entropy of a closed system increases with time'. These statements introduce the thermodynamic concepts of temperature (T) and entropy (S), both of which are parameters determining the direction in which an irreversible process can go. The temperature of a body or system determines whether heat will flow into it or out of it; its entropy is a measure of the unavailability of its energy to do work. Thus T and S determine the relationship between Q and W in the statement of the first law. This is usually presented by stating the second law in the form DU = TDS - W. The second law is concerned with changes in entropy (DS). The third law of thermodynamics provides an absolute scale of values for entropy by stating that for changes involving only perfect crystalline solids at absolute zero, the change of the total entropy is zero.

This law enables absolute values to be stated for entropies. One other law is used in
thermodynamics. Because it is fundamental to, and assumed by, the other laws of thermodynamics it is usually known as the zeroth law of thermodynamics. This states that if two bodies are each in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other.
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THERMOGRAPH

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A thermograph is a self-registering device for recording fluctuations in air temperature (thermometer). Various forms of thermograph have been made, traditionally they registered the temperature on a clockwork revolving drum sometimes with a pen which traces a curve and sometimes photographically.
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THERMOLUMINESCENCE

Thermoluminescence is the luminescence produced in a solid when its temperature is raised. It arises when free electrons and holes, trapped in a solid as a result of exposure to ionising radiation, unite and emit photons of light. The process is made use of in thermoluminescent dating, which assumes that the number of electrons and holes trapped in a sample of pottery is related to the length of time that has elapsed since the pottery was fired. By comparing the luminescence produced by heating a piece of pottery of unknown age with the luminescence produced by heating similar materials of known age, a fairly accurate estimate of the age of an object can be made.
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THERMOMETER

A thermometer is a device used to measure temperature. It was invented by Galileo in 1592. The graduation and inclusion of fixed points was added by Sanctorio who used snow and the heat of a candle, dividing the range obtained into degrees. The first sealed thermometer was made by Ferdinand II, the Grand Duke of Tuscany, in 1654. He filled the bulb and part of the tube with alcohol and then melted the glass tip, thereby sealing the tube. In England, Boyle, at the request of the Royal Society, made experiments on thermometers, his lectures on cold being published in 1665. Mercurial thermometers were first employed by the Academia del Climento of Florence in 1657. In 1694 Renaldini suggested the boiling-point of water as the upper limit of the scale.

In 1706 Fahrenheit made improvements to the thermometer. In 1714 he made his Fahrenheit thermometer with three fixed points. He arrived at his zero by taking a mixture of ice water and sal ammoniac; the second point he obtained by mixing ice and water - this point he called 32 degrees, or freezing point, his third mark was blood heat and was obtained by placing the thermometer in the mouth of a healthy man and holding it there until it reached the body temperature. He then divided the distance between the melting point of ice - 32 degrees - and the boiling point of water - 212 degrees - into 180 degree marks.

Celsius invented his own scale with the boiling point of water at zero and the freezing point of water at 100 degrees, this scale has now been inverted. In France and other parts of Europe, and in all scientific investigations, the Centigrade or Celsius scale is used. Reaumur's thermometer, as used in Germany, has the space between the freezing and boiling points divided into 80 equal parts, the zero being at freezing.
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THERMOPILE

A thermopile is a series of thermocouples, first developed in the 19th century, closely packed together to combine their effect, especially arranged for measuring small quantities of radiant heat.

The original thermopile was invented by Melloni and was used for investigating small increments of heat and in the process the diathermancy of bodies. Several pairs of antimony and bismuth bars were placed in a brass case with wires connected from their poles to a sensitive galvanometer. The extremities of the bars being exposed to a source of radiant heat, while the temperature of the other extremities of the bars not being altered, a current of electricity, proportional to the quantity of heat falling upon the exposed extremities of the bars, passed through the wires from the poles of the pile, and caused the magnetic needle of the galvanometer to deflect more or less according to the quantity of electricity circulating.

In use, the source of radiant heat was positioned behind a screen with an aperture, the aperture being filled with a slice of an object for measuring its diathermancy (transparency to heat), the heat from the source reaching the bars solely through the object under test. Experiments conducted in the 19th century showed that colourless rock-salt was highly diathermanous, allowing more heat to pass through it (92 per cent) than colourless plate glass which arrests 60 per cent of the heat transmitted, while water is very opaque to radiated heat, arresting 89 percent of the radiant heat.
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THERMOSTAT

A thermostat is a device which automatically maintains temperature at a constant value or gives notice of an undue change in temperature.
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THIAMINE

Thiamine is vitamin b1 a deficiency of which causes beriberi.
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THIAZINE

The thiazines are compounds containing a ring of one nitrogen, one sulphur, and four carbon atoms.
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THIO-DERIVATIVE

A thio-derivative is a compound in which sulphur has replaced an equivalent amount of oxygen, such as potassium thio-cyanate, KCNS, in which the sulphur has replaced the oxygen in potassium cyanate, KCNO.
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THIOPHENE

Thiophene is a colourless, volatile liquid closely resembling benzene. It occurs in coal-tar and is extracted by shaking with concentrated sulphuric acid. Thiophene is a parent substance of a number of derivatives.
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THIXOTROPIC PAINT

Thixotropic paint is a paint which has a jelly-like structure which is broken down when the paint is stirred, shaken, heated or when it is subjected to the shearing action of a brush or roller, and which returns to its jelly-like state a short time after the action ceases. Thixotropic paints claim the advantage that they require no stirring before use, that no settlement takes place during storage and they are easy to apply, being non-drip.
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THOMAS-GILCHRIST PROCESS

In metallurgy, the Thomas-Gilchrist Process was an important improvement on the Bessemer process of producing steel. It was devised by Sidney Gilchrist Thomas, a magistrate's clerk in London, and put into practical shape by him in conjunction with his cousin, Percy W Gilchrist, a chemist at Blaenavon Ironworks in Wales, where the process was first tried about 1877. The aim of the process is to eliminate phosphorus from the steel produced, and thus to permit the use of pig irons containing the normal proportions of that element. The phosphorus is removed from the molten iron in the converter and concentrated in a slag by adding an excess of lime as flux, the lining of the converter being prepared of a basic material such as dolomite limestone, instead of an acid material such as the ordinary siliceous firebrick. Hence the process is often described as the basic process, and the product as basic iron or steel. The process gives rise to a valuable by-product known as Thomas or phosphatic slag fertiliser.
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THORIUM

Thorium is radioactive metal element of the tin group with the symbol Th. Thorium was discovered by Berzelius in 1828. It occurs principally in thorite and other rare minerals. It was formerly isolated by displacement by potassium fluothorate, and is a grey metallic powder. It burns brightly in oxygen.
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THREE-COLOUR PROCESS

The three-colour process is a method of making prints in natural colours by photographic or mechanical printing. The term is more widely used in the latter sense, and is employed to denote printing by the half-tone process in three colours. The basis of the three-colour process is the making of three negatives through red, green and blue-violet filters from which three prints are then superimposed to produce the final natural print. In mechanical printing three printing plates are used impressions from each of which are printed successively in the respective ink on a printing machine.
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THRESHING-MACHINE

A threshing-machine is a powered machine for separating grain from the straw. The threshing-machine was invented in Scotland in 1758 by Michael Stirling, a farmer in Perthshire; it was afterwards improved by Andrew Meikle, a millwright in East Lothian, about the year 1776. Since that time it has undergone various improvements. The principal feature of a threshing-machine is the rotary drums or cylinders, which receive motion from an engine (in early machines powered by a water wheel, horse or oxen). The first drum which comes into operation has projecting ribs called beaters on its outer surface, parallel to its axis. This drum receives a very rapid motion on its axis. The sheaves of corn are first spread out on a slanting table, and are then drawn in with the ears foremost between two feeding rollers with parallel grooves. The beaters of the drum act on. the straw as it passes through the rollers, and beat out the grain. The threshed or thrashed straw is then carried forward to two successive drums or shakers, which, being armed with numerous spikes, lift up and shake the straw so as to free it entirely from the loose grain lodged in it. The grain is made to pass through a grated floor, and is generally conducted to a winnowing-machine connected by gearing with the threshing-machine itself, by which means the grain is separated from the chaff.
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THROTTLE

In engineering, a throttle or throttle valve, is a valve for regulating the supply of fuel - steam, gas, petrol etc - to an engine.
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THROW

In engineering, the throw is the distance between the axis of a crank-pin and the axis of the crank-shaft; or between the centre of the eccentric and the axis of the shaft on which it is mounted. The throw of an engine crank is one-half the travel of the piston that drives it; that of an eccentric one-half the travel of the back-end of the eccentric rod.
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THULIUM

Thulium is a rare metal element with the symbol Tm. Thulium was first discovered in 1879, but was not isolated until 1900. It is found in euxenite, samarskite, ytterspar and some other minerals.
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THUNDER

Thunder is a loud noise which accompanies lightning, but appears to follow it due to the difference at which sound and light travel. Thunder is the noise which occurs due to the disruption of the air by the electrical discharge (lightning), which at five times the heat of the sun actually causes the air to explode.
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THYMOL

Thymol (methyl-propylphenol) is a white crystalline phenol obtained from the oil of thyme, particulary Thymis vulgaris, and also from the oils of horsemint and ajowan. It has a pleasant aromatic smell and is used as an antiseptic and deodorant. Thymol is a strong antiseptic and has the advantage over phenol that it doesn't burn the skin.
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TIDE-MILL

A tide-mill is a kind of water-mill turned by the action of the tide.
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TIFF

TIFF (Tag Image File Format) is a now dated format of bitmap image file developed by the Aldus Corporation for data exchange between desktop publishing and related computer applications, notably high quality exchange between the displayed and printed pictures.
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TILT-HAMMER

The tilt-hammer was a large and heavy hammer worked by steam or water power, and formerly used in forgings. By the start of the 20th century it had been largely superseded by the steam-hammer, but it was still advantageously used with light work. Cogs being brought to bear on the tail of the hammer, its depression caused the head to be elevated, which, when the tail was liberated, fell with considerable force by its own weight.
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TIME

Time is the general idea of successive existence, or that in which events take place, space being that in which things are contained. Relative time is the sensible measure of any portion of duration, often marked by some phenomenon, as the apparent revolution of the celestial bodies, more especially of the sun, or the rotation of the earth on its axis. Time is divided into years, months, weeks, days, hours, minutes, and seconds; but of these portions the years and days only are marked by celestial phenomena. The instruments employed for measuring time are clocks, watches, chronometers, hourglasses, and dials; but the three first are those chiefly used.
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TIME 2

Time were an English PC assembler and retailer. They were established during the 1980s and grew into a nationwide organisation with showrooms over the whole country. They assembled and supplied a range of standard PCs aimed at the retail market.
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TIMESLIPS PLUS

Timeslips Plus is a computer program designed to keep track of billable time. It is ideal for law offices or consultants, or for Information Centres that use a charge-back system. Timeslips Plus can be run memory-resident so you can access it while running other applications. When you begin a billable task such as a client phone call, call up a time slip and start the timer. When you stop the timer, you see how much time has elapsed. (If you prefer, you can input time manually without using the automatic timer.) Timeslips Plus also prepares professional-looking invoices in minutes which can be easily customised. The product lets you determine what information appears on the invoice and how it will be presented. Options include Bill, No Charge, Do Not Bill, Summary, and Work in Process. In addition, you can set minimum, maximum, or absolute fees for a project or case, no matter how many bills are sent. You can customise bills for each client to show as much detail as appropriate.

The product lets you create expense slips for out-of-pocket expenses. Through a menu-driven interface, Timeslips Plus allows you to print a report that evaluates performance based on the variance between actual and estimated time. Many other business and financial reports can be generated, along with more than 30 graphs and charts. Timeslips Plus can be customised to your particular application needs. Main headings default to User, Account, and Activity, but you can rename them as desired. The product can accommodate up to 250 individual users, 250 billable activities, and up to 3,400 accounts.
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TIN

Tin is a hard, white, ductile metal with an atomic weight of 119 and the chemical symbol Sn (from the Latin stannum).

Tin appears to have been known in the time of Moses; and the Phoenicians traded largely in the tin ores of Cornwall. The mountains between Galicia and Portugal, and those separating Saxony and Bohemia, were also productive of tin centuries ago, and still continue. Tin occurs in the Malay Peninsula, the island of Banca, India, Mexico, Chile, Peru, the United States, Australia, Africa, etc.

There are only two ores of tin: the native dioxide, called tin-stone or cassiterite; and the double sulphide of tin and copper, called tin-pyrites. The former is the only ore used for obtaining metallic tin. It occurs either in the massive form or as distinct quadratic crystals which have a dark-brown colour and metallic lustre. It is usually contaminated with copper sulphide, arsenical pyrites, and tungsten compounds. It is found in veins in metamorphic or igneous rocks, such as granite, porphyry, slate, etc, and is then known as mine-tin, or sometimes in alluvial deposits formed by the denudation of the above veins, and is then known as stream tin. The ore is first ground and washed, and then roasted in a reverberatory furnace to expel the sulphur and arsenic. Mixed with limestone and fuel, it is again fused in a furnace for about eight hours, the earthy matters forming a slag with the lime, while the oxide of tin, reduced to a metallic state, falls by its own weight to the bottom, and is drawn off. The tin, still impure, is again moderately heated, when it melts and flows off into the refining basins, leaving the greater part of the foreign metals in a solid state. The molten tin is stirred with a wooden pole, and, when partially cool, it separates in zones, the upper consisting of nearly pure tin, while the under is so impure that it must be melted again. The upper layer is removed, cast into blocks, and sold as block-tin, the purest specimens being called refined-tin.

Pure tin has a fine white colour like silver. It has a slightly disagreeable taste, and emits a peculiar sound when rubbed. Its hardness is between that of gold and lead, and it is very malleable. Specific gravity 7.29. Melting point about 233 degrees Celsius. Tin is very flexible, and when bent emits a crackling sound, sometimes called the cry of tin. It loses its lustre when exposed to the air. At very low temperatures it passes spontaneously into another modification known as gray-tin this has a specific gravity 5.8, and falls to a powder. Ordinary tin can be rolled out into very thin sheets known as tin-foil. Oxygen combines with tin, forming protoxide of tin or stannous oxide, and dioxide or stannic oxide. The compounds of chlorine with tin are dichloride or stannous chloride, and stannic chloride. Stannic chloride has long been known as the fuming liquor of Libavius, so called from Libavius, a chemist of the 16th century. Stannic sulphide has long been known in chemistry as aurum mosaicum or mosaic gold.

Tin unites with arsenic and with antimony, but not readily with iron. Alloyed with copper it forms bronze, bell-metal, and several other useful alloys. With lead it forms pewter and solders of various kinds. Tin-plate is formed by dipping thin steel plates into melted tin after being coated with a layer of grease; they are afterwards rolled and the grease removed by bran. Tin is principally employed in alloys. Its oxides are used in enamelling, and for polishing metals, and its solution in nitro-muriatic acid is an important mordant in dyeing, rendering several colours, particularly scarlet, more brilliant and permanent.
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TIN-PLATE

Tin-plate is a sheet of wrought iron or mild steel that has received a thin coating of two or three percent of tin by immersion in the molten metal to protect it from rust. Tin-plate is used in cans for food and drink. Tin-plate was first manufactured in great Britain around 1670 having been invented in Bohemia early in the 16th century.
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TINT

Tint is what is produced when a colour is lightened or reduced by the addition of white.
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TINY ENCRYPTION ALGORITHM

Tiny Encryption Algorithm (TEA) is a secret key cryptography method developed by David Wheeler and Roger Needham of the Cambridge Computer Laboratory. The method uses a 128-bit key and utilises the block cipher method to break text into 64-bit blocks before encrypting them.
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TITANIUM DIOXIDE

Titanium dioxide (also known as titanium white) is a substance used as a very strong white pigment produced from the mineral limonite and occurring naturally as the mineral rutile. It is a brilliantly pure white with enormous staining strength. Titanium dioxide is chemically inert and does not react with oil or varnish media of high acidic value and is resistant to chemicals in the atmosphere.
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TITRATION

Titration is the analysis or determination of the concentration of a solution by adding measured amounts of a standard solution of a suitable reagent until the chemical reaction between the two solutions is completed. The completion of the reaction between the two solutions is determined usually by a change of colour, often of a third substance, e.g. litmus, which is termed an indicator.
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TOGGLE-BOLT

A toggle-bolt is a kind of wall fastener for use on open-backed plaster boarding etc, having a part that springs open or turns through 90 degrees after it is inserted, so as to prevent withdrawal.
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TOGGLE-JOINT

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A toggle-joint is an elbow or knee joint consisting of two bars so connected that they may be brought into a straight line, and made to produce great end-wise pressure.
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TOLUENE

Toluene (toluol, methyl-benzene) is a hydrocarbon, colourless liquid similar to benzene derived from petroleum and coal-tar. It has been used as a thermometric liquid.
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TOLUIDINE

Toluidine (Methyl-aniline) is a colourless, oily, fluid substance prepared from nitrotoluene. There are three isometric toluidines, the ortho-, meta- and para-toluidine, the orthotoluidine being the most important. Orthotoluidine differ from the other toluidines in giving a green colour with ferric chloride and paradiamidobenzene. Paratoluidine is a solid. The toluidines are employed in the manufacture of aniline dyes.
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TOMBAC

Tombac or tombak, also known as Muntz metal and patent metal, is a full yellow coloured metal alloy. It is a kind of brass containing 75 to 85 percent copper and 25 to 15 percent zinc invented in 1832 by G F Muntz of Birmingham. It was used as an imitation of gold for cheap jewelry, for sheathing ships and for other purposes. When arsenic is added it forms white tombac.
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TONE

In colour, tone is the amount of light reflected from a surface of colour, irrespective of all other characteristics.
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TONKA BEAN

The tonka bean is the fruit of a Guiana shrub. It is used in perfumery.
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TONOMETER

A tonometer is a contrivance for the exact measurement of musical pitch. The original tonometer, invented by Scheibler, consisted of 52 tuning forks laboriously corrected by counting the beats and by comparison with the results obtained from the monochord, so as to provide an accurately tuned scale from any given pitch.
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TOPOGRAPHY

Topography is the art or science of geographical description. That is giving the situation, natural features, buildings etc of a country and also describing the rivers, mountains etc.
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TOPS-10

TOPS-10 was DEC's proprietary OS for the fabled PDP-10 computer, long a favourite of hackers but now effectively extinct.
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TORQUE

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In mechanics, torque is a force, or combination of forces, that tend to produce a rotating or twisting motion; forces producing rotation. For example, when tightening or loosening a nut and bolt, one turns the nut and the strength or force required to turn the nut is known as torque. Similarly, in a motor vehicle, the force provided for turning the wheels is known as torque (it is rotating the wheels).
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TORQUE WRENCH

A torque wrench is a tool for setting and adjusting the tension of nuts and bolts.
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TORSION

In mechanics, torsion is the strain produced in a solid body when parallel planes are turned relatively to one another round an axis perpendicular to them. If one end of a cylindrical wire is kept fixed and the other end is twisted by a mechanical force, and if under this twisting stress the wire turns through an angle, then it is found that, so long as the angle is not too great, it is proportional to the applied force, that is if the applied force or couple is doubled, the angle through which the end of the wire is twisted is also doubled.

If the length and radius of the wire are known, and also the strength of the twisting force, then the angle through which the wire twists varies directly with the length of the wire multiplied by a constant depending upon the material of the wire. Since the angle varies inversely as the fourth power of the radius of the wire, the deflection produced by the twisting force increases very rapidly as the wire becomes smaller, for example if the wire's radius is halved the angle of twist is multiplied by 2 to the power of 4, or in other words 16. In measuring small torsions, therefore, a very thin wire or thread is chosen, and for this purpose quartz fibres of extreme tenuity are employed.
Most substances behave very differently in their ability to recover from torsion. Quartz, steel, glass etc will suffer a considerable torsion and when it is removed regain their original forms. Copper and lead on the other hand, will not recover from even small twists.
One of the important applications of torsion is in a spring, and it is because of its ability to recover that steel is typically used for springs.
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TORSION BALANCE

A torsion balance is an instrument which was invented by Coulomb for measuring electric and magnetic attraction. A fine silver wire supports, at its centre of gravity, a horizontal carrier with bodies of known electric charge at each end, or a magnet of known strength. The deflection of the carrier determines the strength of the attractive force when the source of attraction is placed at a known distance from it.
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TOUCHSTONE

A touchstone is a device for roughly ascertaining the purity of gold alloys. It consists of a smooth strip of hard black stone, on which a corner of the alloy is rubbed so as to leave a streak, which is then moistened with an acid composed of 78.4% nitric acid, 1.6% hydrochloric acid and 20% water. By comparing the effect with that produced on streaks made with alloys of known compositions, an approximation to the gold content of the alloy is found.
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TOXOL

Toxol is an explosive comprised of a mixture of trinitrotoluene and trinitroxylene.
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TRACEROUTE

Traceroute is a computer program for the Unix platform that attempts to trace the route an IP packet would follow to some Internet host. It traces the route by launching UDP probe packets with a small time to live (ttl) and then waiting for an ICMP 'time exceeded' reply from a gateway.
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TRACTOR

A tractor is a power-driven machine adapted to haul other machines or vehicles over roads or rough ground.
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TRACTRIX

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A tractrix is a curve whose tangents are all of equal lengths, the involute of a catenary.
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TRAGACANTH GUM

Tragacanth gum is a partly water-soluble gum exuded by the tree Astragalus verus and used as an adhesive and in medicine for the preparation of emulsions.
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TRAMMEL

A trammel is an instrument for drawing ovals, used by joiners and other artificers. One part consists of a cross with two grooves at right angles; the other is a beam-compass carrying two pins which slide in those grooves, and also the describing pencil.
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TRANSCEIVER

A transceiver is a combined radio transmitter and receiver sharing a common housing and many of the same components.
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TRANSDUCER

A transducer is a device which takes in power from one part of a system and emits power of a different kind to another part.
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TRANSFORMER

A transformer, a machine for producing from an electric current another of a different kind. The first transformer was made by Faraday in 1831. A transformer may be used to raise the potential or voltage of an electrical supply (step-up transformer) or to lower it (step-down transformer)', to change an alternating current into a direct current or vice versa; or to produce polyphase alternating currents from single-phase ones or vice versa. Transformers are of two main types: static transformers, in which no part rotates, and rotary transformers or converters, in which there is a rotating part. The rotary converter is substantially a direct-current dynamo with a closed winding. The common alternating-current transformer consists of two insulated electric circuits wound on a common iron core. The coil carrying the current to be transformed is called the primary, and the other the secondary. In the shell type the magnetic circuit encloses the windings ; in the core type the windings enclose the magnetic circuit. Transformers form an essential part of the equipment of electric power and lighting stations.
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TRANSISTOR

A transistor is an electronic component made of a semiconductor material and three or more electrodes.
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TRANSIT

In astronomy, a transit is (a) the passage of a heavenly body across the meridian of any place, a phenomenon which is usually noted by a transit instrument. The determination of the exact times of the transits of the heavenly bodies across the meridian of the place of observation enables the astronomer to ascertain the differences of right ascensions, and the relative situations of the fixed stars, and the motions of the sun, planets, and comets, in respect of the celestial meridians. (b) The passage of one heavenly body over the disc of a larger one; but the term was chiefly restricted to the passage of the inferior planets, Mercury and Venus, over the sun's disc. The transits of Venus were formerly of great importance in astronomy, as they afforded the best means of determining the sun's parallax, and consequently the dimensions of the planetary system.
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TRANSIT CIRCLE

In astronomy, a transit circle is an instrument for ascertaining the time of star transits across the meridian. The transit cirlce was invented by Olaus Romer in 1690, and consists essentially of a telescope movable in the plane of the meridian, and supported on two pillars which are respectively east and west of it. On one side of the telescope is a fixed circle which denotes its movement in the plane of the meridian, and which is read by miscrosopes fixed to one of the supporting pillars. On the other side of the telescope is a circle which is used for moving it.
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TRANSLATOR

In radio terms, a translator is a device that receives multiple signals within a certain frequency range and simultaneously retransmits them in another frequency range.
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TRANSMISSION OF HEAT

If a steel poker is pushed into the fire and left there for a time the handle becomes warm. Heat travels through the metal by a process called conduction. This process is complex. It differs between metals and non-metals. When a metal is heated the free electrons which it contains begin to move faster, i.e., their kinetic energy increases. The hot electrons then drift towards the cooler parts of the metal and at the same time there is a drift of slower-moving (cooler) electrons in the reverse direction. In those substances where no free electrons are present the process of conduction is entirely different. In such cases the heat energy is conveyed by longitudinal waves, similar to sound waves, but of considerably higher frequency. These waves are transmitted in tiny energy packets called 'phonons'. Most metals are good conductors of heat; silver and copper are exceptionally good. On the other hand, substances such as cork, wood, cotton and wool are bad conductors. Both good and bad conductors have their uses.

The best kettles, other than electric kettles, are made of copper, since heat is conducted most rapidly through this metal. The 'bit' of a soldering iron is also made of copper, so that when its tip is cooled through contact with the work, heat is rapidly conducted from the body of the bit to restore the temperature of the tip and maintain it above the melting point of solder. Bad conductors have a very wide application. Beginning with our personal comfort, we prevent loss of heat from ourselves by a covering of poorly conducting material. Textiles are bad conductors of heat, since they are full of tiny pockets of air enclosed by the fibres of the material. Air, in common with all gases, is a very bad conductor of heat. It is usual to say that wool is warmer than cotton. Technically, of course, we imply that it has a lower thermal conductivity than cotton. A stone floor feels cold to the bare feet, but a carpet on the same floor feels warm. This difference arises from the fact that stone is a better conductor of heat than a carpet. To begin with both the stone floor and the carpet are at the same temperature. Since the feet are warmer than either, heat tends to flow from the feet. Stone, being the better conductor, conveys heat away from the feet more rapidly than the carpet. Consequently, the feet feel cold on the stone but warm on the carpet. Precisely the same effect is experienced when handling a garden fork in winter. The iron part of the fork feels cold, but the wooden handle warm.

Loss of heat by conduction through the walls of an oven is reduced by constructing it with double walls. The space between is packed with slag wool or glass fibre. These substances are not only very poor conductors but also have the merit of being non-inflammable. Material of low thermal conductivity used for the purpose of preventing heat loss is called lagging. Another example is the covering of hot-water storage tanks and pipes with a layer of plaster mixed with asbestos or other insulating material. Similarly, cold-water pipes may be lagged with strips of felt or sacking to prevent freezing during very cold weather.
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TRANSPONDER

A transponder is a device that will emit a radio signal when it receives a radio signal on a certain frequency.
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TRANSURANIC

Transuranic is a chemical term referring to artificially manufactured elements which have an atomic number higher than uranium.
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TRANSVERTER

A transverter is a device that takes one radio signal in a specified frequency range and simultaneously retransmits it in another frequency range. (This differs from a translator, which can handle more than one signal).
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TRAPEZIUM

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In geometry, a trapezium is a plane figure comprised of four straight lines of which one pair of opposite sides only are parallel.
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TRAPEZOID

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In geometry, a trapezoid is an irregular plane figure comprised of four straight lines in which none of the sides are parallel.
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TREADLE

A treadle is a foot operated lever used to impart motion to a machine, such as a sewing-machine or lathe for example.
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TREADMILL CRANE

A treadmill crane was a simple, but ingenious device used for hoisting large blocks of stone up to great heights when building castles and cathedrals etc during the Mediaeval period and beyond to the 18th century, throughout Europe. The treadmill crane comprised a large wooden cylinder, open at one side, about 210 cm in diameter with a stout wooden spindle in the centre. This cylinder was mounted at the top of the structure being built, and turned by two or three men walking the treadmill, which caused the spindle to rotate. Fixed to the spindle was a stout rope which was turned on to the spindle by the rotation, and so hoisted up what ever was attached at the lower end. By using treadmill cranes, Mediaeval builders in the 13th century were able to hoist blocks of stone weighing two tons and more to the great heights of Salisbury Cathedral spire and the great castles of England.
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TRIAC

A triac is a bi-directional thyristor used in A.C. control circuitry.
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TRIANGLE

In geometry, a triangle is any figure formed by three intersecting lines. When the lines are straight the triangle is a plane triangle. In spherical triangles, the sides are arcs of great circles of a sphere. Triangles are called equilateral, isoceles and scalene, according as all three sides are equal, two sides are equal, or all sides are unequal. The first book of Euclid is concerned chiefly with the properties of plane triangles, and from the study of such properties arose the science of trigonometry. The area of a plane triangle is half the length of the base multiplied by the altitude of the apex or the square root of s(s-a)(s-b)(s-c) where a,b and c are the lengths of the sides, and s is half their sum.
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TRIANGULATION

Triangulation is a technique employed in surveying. A base-line is set out in a convenient and level situation and measured with great accuracy. A theodolite is then set up at each end of the base- line, and readings are taken on some prominent point or beacon, giving the angular displacement of the beacon relative to the base-line. A triangle is thus formed, of which the size of the angles and the length of one side are known, and therefore the length of the remaining sides may be calculated.
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TRICHLOROETHANE

1,1,2-Trichloroethane is a colourless, sweet-smelling man-made liquid that is predominantly used where 1,1-dichloroethane (vinylidene chloride) is manufactured. It may also be formed in landfills when 1,1,2,2-tetrachloroethane is broken down. 1,1,2-Trichloroethane is used as a solvent where its high solvency is needed, such as for chlorinated rubbers. It may be used as a solvent for fats, oils, waxes, and resins. 1,1,2-Trichloroethane may be found in some consumer products. 1,1,2-Trichloroethane will not burn and has a higher boiling point than water. When it is released into the environment, it eventually ends up in the atmosphere or groundwater. Reaction in both the atmosphere and groundwater is very slow. In the air, half of the chemical is expected to degrade in 49 days and will disperse far from where it is released before degrading. There is no breakdown of 1,1,2-trichloroethane below the soil surface in groundwater within 16 weeks; some experiments suggest that it will persist for years. 1,1,2-Trichloroethane is soluble in alcohol, ether, and chloroform.
1, 1,2-trichloroethane is also known as ethane trichloride; trichloroethane; vinyl trichloride; and 1,2,-trichloriethane.
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TRICHLOROETHYLENE

Trichloroethylene is a colourless liquid at room temperature with an odour similar to ether or chloroform. It is a man-made chemical that does not occur naturally in the environment.
Trichloroethylene is a powerful chlorinated solvent mainly used as a solvent to remove grease from metal parts - commonly prior to painting. It is used as a solvent in other ways, too, and is used as a chemical building block to make other chemicals.
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TRIDECAGON

A tridecagon is a thirteen-sided polygon.
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TRIETHANOLAMINE

Triethanolamine is normally used as an auxiliary emulsifying agent after in situ reaction with a fatty acid in the preparation of cosmetic emulsion products such as creams and lotions. It has several disadvantages not least that of discolouring easily in the presence of trace metal contaminants and even on simple exposure to air.
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TRIMETHYLAMINE

Trimethylamine is a tertiary amine, that occurs in herring brine and the blossoms of hawthorn. It is chiefly obtained as a product of the distillation of the nitrogenous residue left in the preparation of sugar from beetroot. It is a gas with a fishy ammonia-like odour and a strong alkaline reaction. When heated with hydrogen chloride it yields methyl chloride. It is used for preparing pure potassium carbonate from potassium chloride and has also been used in medicine as a cure for gout and rheumatism.
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TRINITRATE

In chemistry, a trinitrate is a compound formed from three molecules of nitric acid by the replacement of the 3 hydrogen atoms by a trivalent element or radical.
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TRINITROTOLUENE

Trinitrotoluene (TNT) is a high explosive.
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TRIO TS711E

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The Trio TS711E was a Japanese two-meter amateur radio scanning transceiver designed for the British market and introduced in 1984. The Trio TS711E covered the 144 Mhz to 146 Mhz amateur band in FM, USB, LSB and CW modes, and had a 40 channel memory.
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TRIODE

A triode is an electronic amplifying valve with three main electrodes (anode, cathode and grid).
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TRIOXIDE

In chemistry, a trioxide is a compound with three atoms of oxygen with an element or radical.
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TRIPLASTITE

Triplastite is a plastic high explosive containing 70 per cent nitrotoluenes, 8 per cent nitrocotton, 22 per cent lead nitrate. It was formerly used for shell filling.
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TRITIUM

Tritium is an unstable isotope of hydrogen. Tritium is radioactive, but considered safer than radium as it is thought that the rays emitted by tritium are unable to penetrate the outer layer of skin on human tissue, or even a thin layer of glass. Tritium replaced radium in luminous paints used for watch dials and the like.
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TROCAR

A trocar is a surgical stylet with a triangular point enclosed in a metal tube and used for withdrawing fluid from a cavity.
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TROFF

Troff is a UNIX formatting and phototypesetting program, written originally in PDP-11 assembler and then in barely-structured early C by the late Joseph Ossanna, modelled after the earlier ROFF which was in turn modelled after Multics' RUNOFF by Jerome Saltzer (that name came from the expression 'to run off a copy'). A companion program, 'nroff', formats output for terminals and line printers. In 1979, Brian Kernighan modified TROFF so that it could drive phototypesetters other than the Graphic Systems CAT. The success of TeX and desktop publishing systems have reduced troff's relative importance.
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TROMPE

A trompe is a water blowing engine. It consists of a long vertical wooden pipe, the lower end of which runs into an air chest. At the top of the pipe is a cone-shaped plug through which water passes. Air enters through holes near the top end, and is forced down into the air chest under pressure by the falling water, the pressure being dependant upon the height of the fall and averaging about one pound per square inch for every two feet of fall. The trompe was a cheap method of working compressed-air engines and machinery in the vicinity of waterfalls. Trompes were chiefly used in America.
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TRONA

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Trona is a naturally occurring hydrous sodium carbonate found in north Africa and America.
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TROPINE

Tropine (methyl-oxyethylpyridine tetrahydride) is an artificial alkaloid obtained by heating atropine or hyoscyamine with baryta-water.
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TROPOSPHERE

The troposphere is the layers of the atmosphere in which, up to a certain height, the temperature falls with increasing altitude.
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TROPOSPHERIC DUCTING

Tropospheric ducting is the propagation of radio signals above 30 Mhz via bending and ducting along weather fronts in the lowest layer of the Earth's atmosphere, the troposphere.
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TRUNKING

Trunking is a method of switching incoming radio signals between different repeater stations to prevent interference and ensure access to a repeater.
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TRY-SQUARE

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A try-square is a tool consisting of a squat, thick, rectangular block handle into which is mounted a rectangular blade at a right angle. The try-square is used by carpenters and joiners for testing the accuracy of right angled (square) work.
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TUBE WELL

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Tube wells, popularly known as Norton's Abyssinian tube wells, were popular around 1900 as a means of collecting water. Tube wells were used when a temporary supply of water was required, and are superior to dug wells which are liable to become foul from surface pollutants.

A tube well is constructed by driving tubes into the soil, one length being screwed onto another, the first tube being perforated at the bottom for about 60 cm, its lower end being furnished with a steel point.

When the subsoil water is reached, a pump is attached to the tube; the water after pumping a short time is clear; the tube forms a cavity which corresponds to the ordinary well at the end of the pipe, owing to the removal of the soil by pumping.

As long ago as the end of the 19th century, the scientist Koch recommended that iron tubes be placed in dug wells and the surrounding space be filled in with cean gravel and sand, the water raised by a pump fixed at the surface.
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TUBERCULIN

Tuberculin was a substance prepared from cultures of the bacilli of tuberculosis. It was introduced by Koch in 1890 and was hoped it would provide a cure for tuberculosis. Results, however, were disappointing.
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TULA-METAL

Tula-metal is an alloy of silver, with small proportions of lead and copper, forming the base of the celebrated Russian snuff-boxes popularly called platinum boxes.
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TUNG OIL

Tung oil (also known as Kukrui oil and China wood oil) is an oil obtained from the seed pods of several varieties of the aleurites or tung tree native to China. Tung oil is pale amber in colour, dull, with an unpleasant smell and taste. It is one of the best drying oils and was used in quick-drying paints and marine varnishes.
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TUNGSTEN

Tungsten (previously also known as wolfram and scheelium) is a grey-white, heavy, high-melting, ductile, hard, polyvalent metallic element that resembles chromium and molybdenum in most of it's properties and is used especially for electrical purposes and in hardening steel. It has the symbol W. Tungsten was first obtained in tungstic acid by Scheele in 1781 and extracted from tungstic acid in 1786 by the De Luyart brothers, and in 1859 was first employed commercially in the making of a new kind of steel.
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TUNGSTEN LAMP

A tungsten lamp is an incandescent electric lamp in which the filament consists of tungsten. Usually a pure tungsten filament is used, but formerly a carbon core coated with tungsten was also used. Tungsten took over from carbon filaments veacsue tungsten has advantages over carbon filaments in giving more light for lower power consumption, being less affected by variations in voltage and remaining at the same candle power for longer than carbon filaments.
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TURBINE

Originally a turbine was a high-speed water-wheel consisting of a horizontal wheel usually constructed with a series of curved floats upon the periphery and driven by a column of water falling into its interior and escaping through oblique channels so as to impel the wheel in the opposite direction. Now, the term turbine is applied to any rotary machine in which a revolving wheel, or a cylinder or disk bearing vanes, is driven by a flow of water, steam, gas, wind, etc, especially such an engine used to generate electrical power.
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TURBOCAD

TurboCAD is a Computer-Aided Design (CAD) program by IMSI Limited for professionals and corporate design departments, but promising ownership costs similar to conventional Office applications such as spreadsheets and databases. The program includes features like extensive customising capabilities and hooks to external database programs. IMSI also hopes to capitalise on AutoCAD's widespread support industry, with a new programming interface which offers compatibility with AutoCAD add-ons.
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TURKEY RED

Turkey red is an artificial red oxide with high opacity, produced by calcining yellow iron oxide at a relatively low temperature. Turkey red is used in paint.
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TURKEY UMBER

Turkey umber is a type of umber obtained from Cyprus, but so called because it was originally exported through Turkey.
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TURNBUCKLE

A turnbuckle is a coupling screwed at both ends, noe end having a right-hand and the other end having a left-hand thread, to which the ends of two bars are screwed. By turning the turnbuckle the screw threads enter further into the screwed sockets, and the bars are drawn nearer together. Turnbuckles are used for applying tension to steel-wire ropes and tie bars.
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TURNBULL'S BLUE

Turnbull's Blue is a pigment produced by the action of a ferrous salt on potassium ferri-cyanide.
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TURNTABLE

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A turntable or turn-table is a horizontal evolving platform used for turning items, such as locomotives, playing vinyl records on old gramophones, etc.
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TURPENTINE

Turpentine (popularly known as turps) is the resinous exudation of various coniferous plants. Turpentine is a valuable solvent, it is clear, limpid and colourless. It evaporates almost completely, leaving no visible residue when exposed in a thin film. Turpentine dissolves all vegetable and mineral oils, but does not dissolve the linoxyn formed by the drying of a paint film, and as such does not disturb previously applied coats of paint making it the ideal solvent for use in paints, though its use declined in preference to cheaper white spirit. All the turpentines dissolve in pure alcohol, and by distillation yield oils, which are termed spirits of turpentine. Oil or spirits of turpentine was used in medicine externally as an excellent rubefacient and counter-irritant, and internally as a vermifuge, stimulant, and diuretic.

Common turpentine is obtained from the Pinus sylvestris or Scotch fir, and some other species of pine. Venice turpentine is yielded by the larch, Larix europcea; Strasburg turpentine by Abies picea or silver fir; Bordeaux turpentine by Pinus maritima or maritime pine; Canadian turpentine, or Canada balsam, by Abies balsamifera or balm of Gilead fir; and Chian turpentine by Pistacia Terebinthus.
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TUTENAG

Tutenag of Chinese white copper, is an alloy of copper, nickel and zinc closely resembling packfong, and used at one time for domestic-ware and fire-grates.
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TUTTLE'S COMET

Tuttle's Comet is a comet with an orbit of fourteen years. It was first recorded by Mechain in 1790, and shown to be periodic by Tuttle in 1858.
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TUTTY

Tutty is a crude zinc oxide obtained chiefly from the flues of zinc-smelting furnaces. Tutty was formerly used in medicine for ointments etc, but now is chiefly used as a polishing powder.
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TUYERE

A tuyere is a terminal of a pipe through which air is supplied to a furnace. It is usually in the shape of a truncated cone, with the smaller end euntering the furnace. Because tuyeres get very hot, and were traditionally made of cast iron, special provision had to be made to prevent it from being burnt or even melted. Tuyeres were made with a hollow wall having an inlet and outlet at the wide end, through which water was circulated to cool the device.
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TWADDELL

A twaddell is a hydrometer for measuring the specific gravity of liquids heavier than water. The twaddell was invented by, and named after, the Scottish scientist Twaddell.
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TWENEX

Twenex was the TOPS-20 operating system by DEC - the second proprietary OS for the PDP-10. TOPS-20 began in 1969 as Bolt, Beranek & Newman's TENEX operating system using special paging hardware. By the early 1970s, almost all of the systems on the ARPANET ran TENEX. DEC purchased the rights to TENEX from BBN and began work to make it their own. The first in-house code name for the operating system was VIROS; when customers started asking questions, the name was changed to SNARK so DEC could truthfully deny that there was any project called VIROS. When the name SNARK became known, the name was briefly reversed to become KRANS; this was quickly abandoned when someone objected that `krans' meant `funeral wreath' in Swedish (though some Swedish speakers have since said it means simply `wreath'; this part of the story may be apocryphal).

Ultimately DEC picked TOPS-20 as the name of the operating system, and it was as TOPS-20 that it was marketed. The hacker community, mindful of its origins, quickly dubbed it TWENEX (a contraction of `twenty TENEX'), even though by this point very little of the original TENEX code remained (analogously to the differences between AT&T V6 UNIX and BSD). DEC people cringed when they heard 'TWENEX', but the term caught on nevertheless (the written abbreviation ` 20x' was also used). TWENEX was successful and very popular; in fact, there was a period in the early 1980s when it commanded as fervent a culture of partisans as UNIX or ITS but DEC's decision to scrap all the internal rivals to the VAX architecture and its relatively stodgy VMS OS killed the DEC-20 and put a sad end to TWENEX's brief day in the sun. DEC attempted to convince TOPS-20 hackers to convert to VMS, but instead, by the late 1980s, most of the TOPS-20 hackers had migrated to UNIX.
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TYNDALL EFFECT

The Tyndall Effect is the scattering of light by fine suspended particles. If a beam of white light is passed through a colloidal suspension of a substance such as mastic in water, light will be emitted at right angles to the beam.
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TYPE

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Type is a rectangular solid of metal, wood, or other hard material having a raised letter, figure, punctuation mark, or other character on the upper end, which, when inked, is used to make impressions on paper and other smooth surfaces; the term is also used collectively. Types must be all of a uniform height, and perfectly true in their angles, otherwise they could not be locked firmly together to be printed from. From the character of the letters types are known as CAPITALS, small or lower-case letters, italics, script, etc. From their size they received the following names, from brilliant, which, however, is rarely used, to English, the largest used in ordinary book-work:

Brilliant, Dianiond, Pearl, Ruby, Nonpareil, Minion, Brevier, Bourgeois, Longprimer, small pica, pica, English, Brevier and Black Letter also known as Old English.

Types are made by casting, the letter being first cut upon the end of a steel punch, and the punch then driven into a piece of copper, which forms the matrix or bottom of the mould intended to produce the letter.
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TYPE METAL

Type metal was an alloy used for type-casting, that is casting the type used for printing. Type metal was usually a mixture of lead and antimony - the antimony added to give hardness - sometimes with the addition of tin, nickel, copper or bismuth.
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TYPEFACE

In printing, a typeface is a design of the characters. Popular typefaces are 'Times', 'Arial' and 'Verdana'. The term 'font' is often erroneously used in computing circles to describe a typeface.
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TYPEMATIC RATE

In computer terms, the typematic rate is how fast keys repeat when held down.
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TYPEMATIC RATE DELAY

In computer terms, the typematic rate delay is the initial delay before key auto-repeat starts. That is how long you've got to press a key before it starts repeating.
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TYPEWRITER

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The typewriter is a machine for printing letters singly on paper which is traversed and moved forward so as to allow writing to be performed. The first patent for a typewriter was filed in 1714 by the Englishman Henry Mills, but the first practical typewriter wasn't invented until 1843 by Charles Thurber. The modern typewriter owes much to the machines produced by Charles Latham Sholes which were adopted by the Remington and Son company of New York, their first machine going on sale in 1874. By the end of the 20th century the typewriter was obsolete, replaced by computerised word processing applications.

Remington's typewriter sold in 1874 had the type-bars pivoted about a horizontal ring, the arms of the type-bars being connected by vertical rods to the levers leading to the keyboard. A rubber cylinder moved the paper, and the impression of the type was supplied by an inked ribbon which unwound automatically from a spool. The pressing down and release of each key in turn moved the paper-carrying cylinder along one space by means of a spring. The roller was moved back and turned ready for the following line by hand. In the original machine each type-bar carried only one character, but later two were introduced on each, and in later machines still three. A shift key enabled any set of characters required to come into operation. By thus economy of keys one set was enabled to print capital and small letters, figures and certain standard punctuation marks, etc. without unduly enlarging the keyboard.

The Remington typewriter was followed by others embodying various new ideas and improvements. The keyboard became standardised, and various standard improvements were introduced such as a back spacing key which enabled the carriage to be reversed one space as necessary to retype a letter; two and three colour ribbons, etc.

Some early typewriters used an ink-pad, the type-bar being pressed against the ink pad before being brought into contact with the paper, but by the later 20th century these were extinct and all typewriters, whether manual or electric were using an inked ribbon.

Quite early some typewriters had their characters arranged on the circumference of a small wheel or small cylinder, which were automatically rotated as the type-key was depressed. Some later typewriters had their characters arranged around a small ball. Many typewriters had the capacity for the entire set of type-bars or type wheel to be interchanged, allowing different sets of characters to be printed.
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TYPOGRAPHIC ETCHING

Typographic etching was a process invented by the Dawson brothers of Chiswick, about 1863, to produce a metal block by means of an electro or cast of the actual lines of a drawing. At first the process was used for landscape, architecture, figures, etc. The introduction of photo-zincography and halftone gradually superseded typographic etching which after 1890 was confined almost exclusively to producing maps, plans etc, before finally becoming obsolete.
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TYRE

A tyre or tire is a hoop, band, or air-filled tube on the rim of a wheel. The steel tyre of a wooden carriage or cart wheel binds the felloes and spokes tightly together, and takes the wear of usage. The tyre is made rather smaller in the first instance, is expanded by heat until it will pass over the felloes, and is allowed to cool, contracting and holding fast. The former rolled steel tyres of railway locomotive carriages and cars were shrunk onto the cast iron or steel centre in a similar way. A projecting lip on the outer face and a ring forced into a groove at the other side, made it impossible for the tyre to move laterally should the shrinkage grip prove insufficient. Railway tyres were about 13 cm broad, at least 2.5 cm thick, and were made of the best steel. The tread was coned to an angle of 1 in 32 towards the outside edge. Flanges were 2.5 cm deep and 2.5 cm wide.

The invention of the bicycle led to the invention of solid rubber tyres which were also used for light carts and heavy automobiles. The tyre was held on the rim by a wire or wires embedded in it, or by beads engaging with flanges in the rim.

The pneumatic tyre became universal by about 1920 and appears to have been invented in 1846 by T Thomson, but credit for the first practical use of the idea is given to J B Dunlop who in 1888 fitted a bicycle with a crude form of air-inflated tyre.

The early pneumatic tyre consisted of two separate parts - an inner air tube of rubber; and an external cover of cotton threads embedded in rubber, and faced with a thick coating of rubber, sometimes protected by steel studs. Rubber treads are corrugated transversely or circumferentially, or in both directions, to minimise slip and skidding. Modern pneumatic tyres, particularly those used on motor cars are without an inner-tube.
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TYRIAN DYE

Tyrian dye was a purple dye derived from animal juice in the shell-fish murex. It was used in ancient times. Since only small quantities could be obtained, it's use was limited to the great and the wealthy, hence purple became the colour associated with majesty.
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