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were found in great abundance in association with these sponges. They were generally of an elongated pyriform shape (the "acerate" form of Bowerbank). He supposed they were originally calcareous, but had become siliceous during the progress of fossilisation.—The next communication was from Dr. Carpenter upon "Different modes of Computing Sanitary Statistics, with special reference to the opinions of Mr. Andrew A. Watt." Upon this subject, which related exclusively to the statistics of population of the city of Montreal, there was an animated discussion.

Naturalists' Society, November 30.—The Rev. J. Crompton, the president, in the chair. Mr. Southwell read a long and interesting paper "On the Flight of Birds." The seeming impossibility of a heavy body supporting itself in mid-air, gliding along, changing its direction at will, apparently violating all the known forces of nature, is sufficiently astonishing to attract the attention and engage the researches of scientific men and yet, till of late, the subject has been neglected, or the theories formed to account for so remarkable a phenomenon have been altogether erroneous. The great stumbling-block to the arrival at the truth seems to have been the very natural idea that buoyancy was; whereas it is now shown, that so far from being an essential, it is an actual impediment. Hunter discovered the presence of air-cells in the bones and dispersed over various parts of the bird's body, and it was believed that by this means heated air was used to render them lighter, and that it was possible by thus inflating the body to increase the bulk, at the same time decreasing the weight; forgetting that additional bulk without a corresponding increase of weight would but enlarge the surface presented to atmospheric resistance, thereby rendering the too buoyant body of the bird the sport of every wind that blows. Sir Charles Bell follows up this idea of excessive lightness; but Captain Hutton, in a paper on "The Birds inhabiting the Southern Ocean," shows that in order to bring the the specific gravity of the albatross to that of the atmosphere, the air-cells in its body should contain 1,820 cubic feet of air heated to 108 degs.—equal to a sphere of more than 15 feet in diameter; or, in other words, they must be 1,200 times the size of the body itself, "which," he adds, "would give it, when flying, an aldermanic appearance which I have never observed." It is obvious, therefore, that the air-cells are not intended to aid the bird in flight by rendering it lighter than the air itself. After referring to the opinions of Sir Charles Bell, Mr. Southwell gave an account of the principles enunciated in France by M. de Lucy, who has shown that three great properties are absolutely essential in all winged animals—(1) weight, or the force of gravity; (2) surface, or the area presented to atmospheric resistance; and (3) force, or the power of projection. Without weight the object might float, but it could never fly, there would be no resisting force to form a fulcrum to its movements, and it would, in fact, be part of the atmosphere and subject to it, wafted hither and thither without the power of resisting. The bird being elevated in the air, possesses, in virtue of its weight, a force always exerting itself in a downward direction, thereby producing motion, which, if it has the power to control, will prove the mainspring of its flight. In order to counteract this downward motion, surface is called into request. The expanded wing is presented to a column of air perpendicular to itself, and a new law of nature comes into operation—that of atmospheric resistance. This is not sufficient to counteract the force of gravity without some mechanical action on the part of the bird, but it would in a great measure break the force of the fall, causing it to descend in a series of zigzags, as a sheet of paper falls from a balloon. We should expect to find the surface increase in proportion to the weight of the animal; but, strange to say, it has been shown by M. de Lucy that the extent of surface is always in an inverse ratio to the weight of the winged animal. The heavier the animal, the smaller its wing surface, referred to a fixed standard. This is shown remarkably in flying insects; the body is very light, but the wing surface is enormous. The bird would soon be brought down from mid-air but for the muscular power of depressing the expanded wing forcibly and rapidly so as to cause the elastic column of the air beneath to rebound with sufficient force to destroy the remaining effects of gravity and so to equalize all the forces as to leave the bird ready to pursue its course at will. The most striking thing about the skeleton of a bird is its great lightness combined with strength. By a beautiful arrangement, the greatest power is given to the wings. The front part of the wing, that first presented to the air in forward flight, is stiff and unyielding, well adapted for cutting its way through the air; the other feathers become weaker and more pliable as they are placed nearer to the body of the bird. The feathers, which are divided into two portions by a nearly central shaft, overlap each other, the anterior web, which is the strongest and stiffest, being uppermost. When the down stroke is delivered, the wing presents to the air an impenetrable and unyielding surface, but when the corresponding up stroke is made, the yielding posterior web of each feather becomes depressed by the resistance of the air above, thus separating the feathers so as to allow of the free passage of the air by this means giving the maximum amount of force to the down stroke, which would otherwise be neutralised by the resistance of the up stroke. But this is not all; the under surface of the wing is more or less concave, while the upper surface is convex. It is obvious, therefore, that when the up stroke is made, the air will rush off and through the wing in all directions, but when the motion of the wing is reversed, the air will be gathered up in its hollow, and the resistance immensely increased. By a wonderful contrivance, the same stroke which elevates the bird gives it a forward motion also. Mr. Southwell then gave an elaborate description of the mode in which forward motion is effected, from the Duke of Argyll's work, "The Reign of Law." Those birds with very long and pointed wings possess the greatest powers of flight; as, for instance, the sharp-winged martin for speed, and the long-winged albatross for both speed and endurance. The power of turning in flight appears to be the result of an involuntary effort, as we turn or incline to the left or right in walking. It is a matter of considerable difficulty to obtain reliable data as to the actual velocity with which birds travel through the air. The flight of a hawk, when its powers are fully exerted, has been calculated at 150 miles an hour; the usual flight of the eider duck at the rate of 90 miles an hour. Audubon estimates the flight of the American passenger pigeon at a mile a minute, and the carrier pigeon to possess, probably, an average of 50 or 60 miles in a long flight, although over short distances, as when pursued by a hawk, its speed is much greater. The flight of rooks, "going to bed with full stomachs," and taking it easy, Major Holland estimates at about 26 to 30 miles an hour; the speed of the albatross whilst coursing in company with a ship, he reckons at about 90 miles an hour. The flight of other birds, such as the swallow, the eagle, and the peregrine falcon, has been estimated as of much greater speed. The power of passing with ease and rapidity over long distances is of vast importance to birds living in communities. Rooks, for instance, would soon exhaust the supply of food in their own neighbourhood. Mr. Stevenson is satisfied that the guillemots and gulls seen feeding in Yarmouth and Lowestoft Roads in summer, come from the great nesting-places on the Yorkshire coast and Mr. Yarrel states, on the authority of Dr. Jenner and the Rev. N. Thornbury, that the domestic pigeons about the Hague "make daily marauding excursions at certain seasons of the year to the opposite shore of Norfolk, to feed on vetches—a distance of forty leagues." Mr. Southwell quoted many instances of the extraordinary power of birds to endure protracted flights; and concluded by saying that man with all his boasted skill has not been able to construct a machine to enable him to navigate the air, and, even with the bird before his eyes, he has failed to learn its lesson. In the discussion which ensued, Mr. Southwell said he hoped his paper would attract attention to the subject of the flight of birds, as very little was known about it; and the very fact that in modern days men attributed the powers of flight in birds to the air-cells being filled with hot air, showed how little the principles of flight must have been considered.

Academy of Sciences, December 20.—M. E. Becquerel presented a note by M. J. M. Gaugain on the electromotive forces developed by platinum in contact with various liquids, The author stated that when two platinum electrodes, not platinised, have remained in an acidulated liquid until they furnish no sensible current, if one of them be washed in distilled water and dried with blotting paper, it becomes negative on being again placed in the liquid. The opposite effect is produced with solution of potash. The effect in the latter case is much greater when the electrodes are platinised. The author ascribed this phenomenon to a modification of the electrodes consisting in a superficial adherence set up between the platinum and the acid or alkaline substance. He also remarked upon the difference of function in platinised and non-platinised electrodes,