Графични страници
PDF файл

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

[merged small][merged small][ocr errors][merged small][merged small][merged small][merged small]

treast-pagueñaror YPE-Light NING CONDUCTOrts-The safe.TY LAMP-ELECTRo-PLATING AND GILDING-This releCTRIC. 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 present. 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 same quantity of fuel. Had he surVol. 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 3-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! It resulted from scientific researches on the properties of solar light, that certain metallic preparations were affected in a peculiar manner 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. * The object of which it is desired to produce a representation, is placed be

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. 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 begreater, 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 icture 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. One of the defects of Daguerreotype, as applied to portraiture, arises from the impossibility of bringing the entire person of the sitter at once into focus. To render this possible, it would be necessary that every part of the person of the sitter should be at precisely the same distance from the lens of the camera obscura, a condition which obviously cannot be fulfilled. It happens, consequently, that those parts of the person of the sitter which are nearest to the lens, will be represented on a scale a little greater than those parts which are most distant; and if the instrument be adjusted so as to bring the nearer parts into very exact focus, the more distant parts will be proportionally out of focus. These defects cannot be removed, but may be so much mitigated as to be imperceptible. By using larger lenses, the camera can be placed at a considerable distance from the sitter, without inconveniently diminishing the size of the pictu.e. PJ this expedient, the difference between the distances of different points of the sitter from the lens, will bear so small a proportion to the whole distance, that the amount of distortion arising from the cause just mentioned may be rendered quite imperceptible. Large lenses, however, when good in quality, are expensive; and it is only the more extensivelyemployed practitioners in this business that can afford to use them. The magnitude of these pictures will, in a great degree, depend on the magnitude of the lens. We have seen, lately, groups executed by a Parisian artist, on plates from fifteen to sixteen inches square." The agency of light and shade has been successfully used, in the same manner, to produce pictures on paper, glass, wood, and other substances, chemically prepared, so as to be more or less impressed with some dark colour. The representations obtained in this manner have not, however, the precision and distinctness which are so universally characteristic of the Daguerreotype process. Attempts have been recently made, with more or less success, to remove the metallic or leaden hue which has

been found disagreeable in Daguerreotype portraits. This is effected by colouring them by means of dry colours rubbed into the incisions made by the action of the light. These coloured Daguerreotypes, though more open to objection on artistical grounds, are, nevertheless, decidedly popular, when judiciously executed. Artists, and especially miniaturepainters, are naturally opposed to Daguerreotype. No miniature, however, will, so far as relates to mere resemblance, bear comparison to a Daguerreotype. The artist can soften down defects, and present the sitter under the most favourable aspect. The sun, however, is no flatterer, and gives the lineaments as they exist, with the most inexorable fidelity, and the most cruel precision. Nevertheless, it is known that some of the most eminent portrait-painters— those whose productions have raised them above petty feelings—do avail themselves of the aid of Daguerreotypes, where well-executed representations of that kind are obtainable; and they see in this no more degradation of their art, than a sculptor finds in using a cast of the subject which his chisel is about to reproduce. But of all the gifts which Science has presented to Art in these latter days, the most striking and magnificent are those in which the agency of electricity has been evoked. From the moment electric phenomena attracted the attention of the scientific world, the means of applying them to the useful purposes of life were eagerly sought for. Although such applications had not yet entered into the spirit of the age as fully as they have since done, it so happened that, in this department of physics, a volunteer had enlisted in the army of science, the characteristic of whose genius was eminently practical, and soon achieved, by his discoveries, an eminence to which the world has since offered universal homage. Benjamin Franklin, a member of a literary society in Philadelphia, had his attention called to the then recent discovery, the phenomena of the Leyden Jar, which at that time astonished all Europe. From that moment the views of Franklin were bent on the discovery of some useful purpose to which these discoveries could be applied. Cui bono was a question never absent from his thoughts. After having made some of those great discoveries which have since formed the basis of electrical science, and have surrounded his name with unfading lustre, he expressed, in a letter to the secretary of the Royal Society of London, in his usual playful manner, his disappointment at not being yet able to find any application of the science beneficial to mankind:—

"The most successful practitioner in Daguerreotype now in Paris is Mr. W. Thompson, an * A picturesque river which washes the Western suburbs of Philadelphia, and to the valley of which it is the custom of the citizens to make pic-nic parties. In the summer months, the temperature at Philadelphia is so high as to banish to the watering-places all who are not abolutely tied to the town by the exigencies of their business.

erican.

“Chagrined a little,” he wrote, “that we have hitherto been able to produce nothing in the way of use to mankind; and the hot weather coming on, when electrical experiments are not so agreeable, it is proposed to put an end to them for the season, somewhat humorously, in a party of pleasure, on the banks of the Schuylkill.” Spirits, at the same time, are to be fired by a spark sent from side to side, through the river, without any other conductor than the water; an experiment which we some time since performed to the amazement of many.f A turkey is to be killed for dinner by the electrical shock, and roasted by the electrical jack, t before a fire kindled by the electrical bottle” (since known as the Leyden phial), “when the healths of all the famous electricians in England, Holland, France, and Germany, are to be drunk in electrified bumpers, under the discharge of guns from the electrical battery.”$

Although the application of the great principles of science to the practical uses of life cannot be too highly appreciated, it would be a great error to carry this enthusiasm for the useful to such an excess as to exclude a just admiration for those high abstract laws, the discovery of which had conferred lustre on the names of our greatest philosophers, and on none more justly than that of Franklin himself. It must be admitted, however, that this

craving after utility was the great characteristic of his mind, and may even be regarded as having been carried almost to a fault. It has been justly observed by a contemporary writer—

“That although the application of the properties of matter and the phenomena of nature to the uses of civilised life is undoubtedly one of the great incentives to the investigation of the laws of the material world, yet it is assuredly a great error to regard that either as the only or the principal motive to such inquiries. There is in the perception of truth itself—in the contemplation of connected propositions, leading by the mere operation of the intellectual faculties, exercised on individual physical facts, to the development of those great general laws by which the universe is maintained—an exalted pleasure, compared with which the mere attainment of convenience and utility in the economy of life is poor and mean. There is a nobleness in the power which the natural philosopher derives from the discovery of these laws, of raising the curtain of futurity and displaying the decrees of nature, so far as they affect the physical universe for countless ages to come, which is independent of, and above all, utility. While, however, we thus claim for truth and kuowledge all the consideration to which, on their own account, they are entitled, let us not be misunderstood as disparaging the great benefactors of the human race, who have drawn from them those benefits which so much tend to the well-being of man. When we express the enjoyment which arises from the beauty and fragrance of the flower, we do not the less prize the honey which is extracted from it, or the medicinal virtues which it yields. That Franklin was accessible to such feelings, the enthusiasm with which he expresses himself throughout his writings, in regard to natural phenomena, abundantly proves. Nevertheless, useful application was undoubtedly ever uppermost in his thoughts; and he probably never witnessed a physical fact, or considered for a moment any law of nature, without inwardly proposing to himself the question, “In what way can this be made beneficial in the economy of life.’”||

After studying the properties of

t This experiment has been recently reproduced in the investigations connected with the electric telegraph, but without giving credit to Franklin as its original author.

t It will be seen by this hint that the idea of applying electricity, as a moving power,

had already occurred to Franklin.

§ Franklin's Works, vol. v. p. 210. Boston: 1837.
| “Lardner on Electricity and Magnetism,” vol. i. p. 41.

« ПредишнаНапред »