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Dublin: Printed by EDWARD BULL, 6, Bachelor's-walk.

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STEAM-DAGUERREOTYPE-LIGHTNING CONDUCTORS-THE SAFETY LAMP-ELECTRO-PLATING AND

GILDING THE ELECTRIC TELEGRAPH.

EACH Succeeding age and generation leaves behind it a peculiar character, which stands out in relief upon its annals, and is associated with it for ever in the memory of posterity. One is signalised for the invention of gunpowder, another for that of printing; one is rendered memorable by the revival of letters, another by the reformation of religion; one epoch is rendered illustrious by the discoveries of Newton, another by the conquests of Napoleon. If we are asked by what characteristic the present age will be marked in the records of our successors, we answer, by the miracles which have been wrought in the subjugation of the powers of the material world to the uses of the human race. In this respect no former epoch can approach to competition with the pre

sent.

VOL. XXXVI.

Although the credit of the invention of the steam-engine must be conceded to the generation which preceded us, its improvement and its most important applications are unquestionably due to our contemporaries. So little was the immortal Watt himself aware of the extent of the latent powers of that machine, that he declared, upon the occasion of his last visit to Cornwall, on ascertaining that a weight of twenty-seven millions of pounds had been raised one foot high by the combustion of a bushel of coals under one of his boilers, that the ne plus ultra was attained, and that the power of steam could no further go. Nevertheless the Patriarch of the steamengine lived to see forty millions of pounds raised the same height by the Had he sursame quantity of fuel. VOL. XXXVI.-NO. CCXI.

vived only a few years longer, he would have seen even this performance doubled, and still more recently it has, under favourable circumstances, been increased in a threefold ratio.

But it is not in the mere elevation of mineral substances from the crust of the globe, nor in the drainage of the vast subterranean regions which have become the theatre of such extensive operations of industry and art, that steam has wrought its greatest miracles. By its agency coal is made to minister in an infinite variety of ways to the uses of society. Coals are by it taught to spin, weave, dye, print, and dress silks, cottons, woollens, and other cloths; to make paper, and print books on it when made; to convert corn into flour; to press oil from the olive, and wine from the grape; to draw up metal from the bowels of the earth; to pound and smelt it, to melt and mould it; to forge it; to roll it, and to fashion it into every form that the most wayward caprice can desire. Do we traverse the deep?-they lend wings to the ship, and bid defiance to the natural opponents, the winds and the tides. Does the wind-bound ship desire to get out of port to start on her voyage?-steam throws its arms round her, and places her on the open sea. Do we traverse the land?-steam is harnessed to our chariot, and we outstrip the flight of the swiftest bird, and equal the fury of the tempest.

It results, from the official returns of the Cornish authorities, that as much power is there obtained from a bushel of coals, as is equivalent to an average day's work of an hundred stage-coach horses.

B

The great pyramid of Egypt stands upon a base measuring seven hundred feet each way, and is five hundred feet high. According to Herodotus, its construction employed an hundred thousand labourers for twenty years. Now we know that the materials of this structure might be raised from the ground to their present position by the combustion of four hundred and eighty tons of coals.

The Menai Bridge consists of about two thousand tons of iron, and its height above the level of the water is one hundred and twenty feet. Its entire mass might be lifted from the level of the water to its present position by the combustion of four bushels of coal!

Marvellous as the uses are to which heat has been rendered subservient, those which have been obtained from light are not less so. Ready-made

flame is fabricated in vast establishments, erected in the suburbs of cities and towns, and transmitted in subterranean pipes through the streets and buildings which it is desired to illuminate. It is supplied, according to individual wants, in measured quantity; and at every door an automaton is stationed, by whom a faithful register is kept of the quantity of flame supplied from hour to hour!

re

It resulted from scientific searches on the properties of solar light, that certain metallic preparations were affected in a peculiar inanner by being exposed to various degrees of light and shade. This hint was not lost. An individual, whose name has since become memorable, M. Daguerre, thought that as engraving consisted of nothing but the representation of objects by means of incisions on a metallic plate, corresponding to the lights and shades of the object represented and as these same lights and shades were shown by the discoveries of science to produce on metals specific effects, in the exact proportion of their intensities-there could be no reason why the objects to be represented should not be made to engrave themselves on plates properly prepared!! Hence arose the beautiful art now become so universally useful, and called after its inventorDAGUERROTYPE.

fore an optical instrument, with which every one is familiar as the cameraobscura. An exact representation of it, on a scale reduced in any required proportion, is thus formed upon a plate of ground glass, so that it may be viewed by the operator, who can thus adjust the instrument in such a manner as to obtain an exact picture of it. If it be desired to make a portrait, the effect of the posture of the sitter can thus be seen, and the most favourable position ascertained before the process is commenced.

The object of which it is desired to produce a representation, is placed be

When these arrangements have been made, the plate of ground glass, on which the picture was previously formed, is withdrawn, and the metallic plate, on which the picture is to be engraved, is substituted for it. This latter being placed in the groove from which the plate of ground glass has been withdrawn, the picture will be formed upon it with the same degree of precision, and in exactly the same position in which it was previously seen on the plate of ground glass.

When the light is favourable, four or five seconds are sufficient to complete the process. According as it is less intense, the necessary time may be greater, but never should exceed a minute. In general, the shorter the time in which a picture is made, the more perfect the picture will be, especially if it be a portrait, because the defects of the representation most commonly arise from the object represented, or some part of it, having shifted its position during the process. In that case, the picture presents the object as though it were seen through a mist. The best portraits we have ever seen produced by this art have been completed in four seconds!

It might be supposed, from what we have here said, that it would be almost impossible, in any case, to obtain a perfect representation of the eyes in a portrait, because of the difficulty of abstaining from winking. It happens, however, that winking being a change of position which is only continued for an inappreciable instant of time, the eye resuming its position immediately, is almost the only movement incidental to a sitter which does not affect the precision of the portrait; unless, indeed, the action of winking were to be continued in rapid succession, which, in practice, almost never occurs.

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