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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.. P 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-paintersthose 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

The most successful practitioner in Daguerreotype now in Paris is Mr. W. Thompson, an

American.

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ally drained a cloud ; but what is not so at when the paper klin, explaining his ructing lightning-conprotection of buildings, wards read before the of London, it was reols of laughter, and was rd as to be deemed uning printed in the "Phiransactions." It was, howd by an independent pubhas attained, as is well world-wide celebrity. long afterwards, the same of the Royal Society who at Franklin's project, were pon to superintend the erecConductors upon the royal pahen, to gratify the royal spleen Last the rebellious philosopher of Revolted colonies, they rejected the ate conductors recommended by nklin, and actually caused blunt Conductors to be placed on the palace. Franklin, who held the office of American Minister in London (the inde. pendence of the United States being then recently acknowledged), on hear

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ing this, wrote to one of his friends in Philadelphia :

"The king's changing his pointed conductors for blunt ones is a matter of small importance to me. If I had a wish about them it would be that he would reject them altogether as ineffectual. For it is only since he thought himself and his family safe from the thunder of heaven that he has dared to use his own thunder in destroying his innocent subjects."†

Art often presses into its service the discoveries of Science, but it sometimes provokes them. Art surveys the fruit of the toil of the philosopher, and selects such as suits her purposes; but sometimes, not finding what is suitable to her wants, she makes an appeal to Science, whose votaries direct their researches accordingly towards the desired object, and rarely fail to attain them.

One of the most signal examples of the successful issue of such an appeal presents itself in the safety-lamp.

The same gas which is used for the purposes of illumination of our cities and towns (and which, as is well known, is obtained from coals by the process of baking in close retorts) is often spontaneously developed in the seams of coal which form the mines, and collects in large quantities in the galleries and workings where the coal-miners are employed. When this gas is mingled

with common air, in a certain definite proportion, the moisture becomes highly explosive, and frequently catastrophes, attended with frightful loss of life, occurred in consequence of this in the mines. The prevalence of this evil at length became so great, that government called the attention of scientific men to the subject, and the late Sir Humphrey Davy engaged in a series of experimental researches with a view to the discovery of some efficient protection for the miner, the result of which was, the now celebrated safetylamp.

Davy first directed his inquiries to the nature and properties of flame. What is flame? was a question which seems until then never to have been answered or even asked.

All known bodies, when heated to a

"Franklin's Works," vol. v. p. 235. Boston: 1837. "Franklin's Works," vol. v. p. 227.

Europe. From that moment the views of Franklin were bent on the discovery of some useful purpose to which these discoveries could be ap. plied. 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 :

"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. A turkey is to be killed for dinner by the electrical shock, and roasted by the electrical jack, 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."§

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

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. must be admitted, however, that this

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"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 knowledge 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 doubtedly 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.'" ||

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After studying the properties of

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.

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

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.

metals, in virtue of which electricity runs along them in preference to other substances, and discovering the property of points to attract the electric fluid, Franklin proceeded at once to the discovery of conductors, or "light ning-rods," for the protection of buildings. "If these things be so,"

wrote he

May not the knowledge of this power of points be of use to mankind in preserving houses, churches, ships, &c., from the stroke of lightning, by directing us to fix on the highest points of those edifices upright rods of iron made sharp as a needle, and gilt (at the points) to prevent rusting; and from the foot of these rods a wire down the outside of the building into the ground, or down round one of the shrouds of a ship, and down her side till it reaches the water? Would not these pointed rods probably draw the electric fire out of a cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible mischief."*

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ing this, wrote to one of his friends in Philadelphia:

"The king's changing his pointed conductors for blunt ones is a matter of small importance to me. If I had a wish about them it would be that he would reject them altogether as ineffectual. For it is only since he thought himself and his family safe from the thunder of heaven that he has dared to use his own thunder in destroying his innocent subjects."†

Art often presses into its service the discoveries of Science, but it sometimes provokes them. Art surveys the fruit of the toil of the philosopher, and selects such as suits her purposes; but sometimes, not finding what is suitable to her wants, she makes an appeal to Science, whose votaries direct their researches accordingly towards the desired object, and rarely fail to attain them.

One of the most signal examples of the successful issue of such an appeal presents itself in the safety-lamp.

The same gas which is used for the purposes of illumination of our cities and towns (and which, as is well known, is obtained from coals by the process of baking in close retorts) is often spontaneously developed in the seams of coal which form the mines, and collects in large quantities in the galleries and workings where the coal-miners are employed. When this gas is mingled with common air, in a certain definite proportion, the moisture becomes highly explosive, and frequently catastrophes, attended with frightful loss of life, occurred in consequence of this in the mines. The prevalence of this evil at length became so great, that government called the attention of scientific men to the subject, and the late Sir Humphrey Davy engaged in a series of experimental researches with a view to the discovery of some efficient protection for the miner, the result of which was, the now celebrated safetylamp.

Davy first directed his inquiries to the nature and properties of flame. What is flame? was a question which seems until then never to have been answered or even asked.

All known bodies, when heated to a

"Franklin's Works," vol. v. p. 235. Boston: 1837. "Franklin's Works," vol. v. p. 227.

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