tures are poor indeed. In some of the Stereoscopic views taken on the Continent, I have noticed that one picture has enjoyed sunlight, whilst in the other some passing cloud has prevented the objects from being depicted in a corresponding manner. There are many other drawbacks connected with a single Stereoscopic camera, but those already named are sufficiently annoying to the operator. These imped iments to success led me to construct a Binocular camera, in which the two pictures could be taken simultaneously, and thus ensure, as far as practicable, uniformity in the results. This camera is in form somewhat like a lenticular Stereoscope. The optical portion consists of a pair of double achromatic lenses, carefully worked alike, and the rackwork of each is connected, so that they both move together for the purpose of adjusting, or focusing, as it is generally called. The cap of each lens is also connected, to enable the operator to open and close them both together with one hand. The dark frame of this camera will hold the ordinary size Stereoscopic glass or plate. If a positive collodion picture is desired, it is advisable to put the prepared surface of the plate towards the back of the camera, instead of towards the lens, as is usual. The picture is thus impressed through the glass on to the prepared surface: collodion positives always appear the brightest on the collodion side. When finished, the picture is covered with transparent varnish, and the other side of the plate blackened. A picture thus taken is correct in position, and decidedly improved in appearance. To focus for a picture of this kind, it is necessary that the ground glass should be reversed in its frame, that the ground side may represent the collodion surface.

This mode of proceeding is applicable to collodion positives, whether Stereoscopic or single, and removes the possibility of injury by the objectionable black varnish, so frequently employed on the collodion

surface.

Pictures taken in the Binocular camera require dividing before they are fitted for the Stereoscope; the left hand picture must be removed to the right hand side. This remark applies to the paper picture from the negative, as well as to positive pictures on glass. Stereoscopic photography is now making very rapid advances; it has been applied to scientific purposes, as well as for those of amusement. Geological, Mineralogical specimens, Crystals, Surgical Anatomy, Machinery and Phrenology are now being successfully illustrated by its aid. There is also a very marked improvement in its application to illustrate scenery. The wonderful pictures, which have been lately taken by that successful Stereoscopic photographer, Ferrier, of the glaciers and scenery of Switzerland, are sufficient, in my humble opinion, to warrant the assertion that Stereoscopic photography is one of the best modes of illustrating the beauties of nature; and should it ever be the good fortune of the photographer to discover the means of fixing the colours as they appear in nature, it would then have reached perfection. There are a number of Stereoscopic pictures on the table, taken in the Binocular camera by Members of this Society; they may be examined by any one interested in this branch of photography.

THE

WEAR AND TEAR OF HUMAN LIFE,

BY THOMAS BRITTAIN, Esq.

[Ax abridged Report of a Lecture delivered at the Manchester Mechanics' Institution.]

MR. BRITTAIN said, no question connected with physical science appeared to be involved in so much mystery as the laws which related to life and death. It was a remarkable fact that a very large portion of the material that comes to the surface of the earth was used to make up organised beings; and by organised beings were meant all things that possessed life, such as trees, animals, and men. It was also a remarkable fact that many thousands of years before the earth was the abode of man, it contained many living beings, exceedingly simple in their construction. If they went down deep enough beneath the surface of the earth they would find there inorganic matter, granite rock; above that they would find one layer above another, all containing the remains of organic bodies, which had been converted into what were termed fossils. A very large portion of these represented beings not at present in existence. Whole generations had been swept away-the entire species had become extinct; so that the animals which now inhabit the surface of the earth are not the animals which inhabited it in early ages,-the vital force in those creatures having become extinct. In the present day they would find the vital force to be very different in different kinds of living things. Some plants would live only for a few hours, while the cedars of Lebanon would last for centuries. Some animals lived but a day or two, while others existed a century or more; and that fact seemed to indicate

that there must be several conditions which go to make up the vital force. All new-born children appeared to have an equal chance of life; but some of them died in a few days-some enjoyed a longer existence, whilst few, and but few, reached old age. There must be cause for those things; and that cause was to be found, not in nature itself, but in obedience to or violation of the laws of life and health. These laws involved several important considerations. One was the necessity of light. Neither plants nor animals could live without a certain amount of light. It was a remarkable fact that if a plant were put in a room, it would be found in a short time to incline towards the window of that room, or, so to speak, to turn its face to the light; and it was also a fact that in narrow, dark streets, lanes, courts, and alleys, there was uniformly a larger proportion of disease than in districts where there was plenty of light and air. A very large proportion of cripples were ascertained to have been born and brought up in courts and narrow streets. There had been discovered a very striking instance of the need of light in a large Russian barracks. One side of the barracks looked towards the south and was light and cheerful, the other side faced the north and it was consequently dark and dreary; it had been ascertained that the soldiers inhabiting the north, or dark side, were uniformly more sickly and diseased than those who lived in the south side. Another consideration was heat, a certain amount of which was requisite for the development of both plants and animals, and for healthy action. Take, for instance, tadpoles or waternewts; if a limb of these creatures was cut off, or mutilated, in warm weather it would speedily be reproduced; but if this were done in cold weather, such reproduction would not take place. In America there was a certain plant, whose native soil was Virginia, there grew to be a large tree, 150 feet high; as it was taken northward it diminished in size to 15 or 20 feet in height, and in the far north it became a mere

it

shrub, rarely exceeding 5 feet. He would next allude to food, and that was a most important subject, and one on which there was the greatest possible diversity of opinion; some people would not eat a beef steak, and others would drink nothing stronger than water, and the divers opinions expressed on the subject by doctors was perfectly ludicrous. Perhaps after all it would be found that no general rule could be laid down with regard to the subject, and that the old proverb was true, that "what was one man's food was another man's poison." Some animals could live without food much longer than others. Man could not live above two or three days absolutely without food, though if supplied with water he might exist twenty days. A spider could live a year without food; and there was a kind of beetle which had been known to live three years without food. In these cases there was very little action, and consequently little necessity for food. The serpent was a lazy animal, it would devour a rabbit, and then wait a month for its next meal, but in its silence there was little wear and tear. He would next refer to sleep. In many cases, such as the oyster, the sponge animal, and others, of the lower form of animal life, there appeared to be a perpetual sleep and unconsciousness; in the oyster there was a very curious organization, very similar to that of the human body, yet it had no consciousness, and but for the existence of animal tissues it might be doubted whether it was an animal at all; so with the sponge, it might be cut or torn asunder, and there was no shrinking, no cringing, no manifestation of feeling, nor yet any indication of consciousness. With regard to the wear and tear of life, food was essential to the nourishment of the tissues. In every motion-in lifting the arm, in speaking, and even in thinking, tissues were worn away, and the more activity there was, the greater was the wear and tear, and the more food was necessary to replenish the tissues. How heartily, for instance, would a hardworking man, after a day's toil, eat food