Page:Supplement to the fourth, fifth, and sixth editions of the Encyclopaedia Britannica - with preliminary dissertations on the history of the sciences - illustrated by engravings (IA gri 33125011196181).pdf/285

 on the Tourmaline, he published, in 1762, a work, in 4to, On the distribution of heat at the surface of the earth; a work which, though translated into French, has hardly, we believe, made its way into this country, and of which we are therefore unable to speak from our own knowledge. He is also the author of many valuable memoirs on different subjects in pure mathematics, in astronomy, mechanics, optics, meteorology, contained in the 7th, 8th, 9th, 10th, and 12th volumes of the Novi Commentarii Petropolitanæ, and in the volumes of the Berlin Memoirs, for 1755, 1756. In a memoir contained in the last of these is the first account of his experiments on the Tourmaline, which were conducted with great accuracy and judgment, and do honour to the author as a man of a sound and philosophical understanding, well instructed in the true principles of inductive investigation. Indeed, notwithstanding the objections we have made to his theories of electricity and magnetism, we must acknowledge that this is the general impression produced by the perusal of his works. He appears to have been well acquainted with practical astronomy, and sometimes to have had the charge of the Imperial Observatory. He made improvements on the Micrometer and the Reticulum, and wrote a memoir on the effects of parallax in the transit of a planet over the sun; a difficult subject, and one rendered at that time (1764) peculiarly interesting, on account of the transit of Venus which was just past, and that which was soon expected. (Novi Com. Pet. Tom. X. p. 433.) In the same volume he has a memoir on the subject of accidental colours, which at that time had hardly been treated of by any author but Buffon; and another on the affinity between electricity and magnetism. In the 12th volume he notices, we believe for the first time, the electric property of the Brasilian emerald. He was not aware that this emerald is in reality the green Tourmaline (Brogniart, Tom. I. p. 418.); a variety of that mineral on which he had already exercised his ingenuity with so much success.

It is rare, in an advanced state of science, to have the satisfaction of making a new discovery with regard to a subject quite elementary, and one that has been long a subject of attention. This, however, happened to Æpinus with respect to the Lever, and to the simplest kind of lever—that which has equal arms; of which he has demonstrated a new property in the 8th volume of the Commentaries above referred to. It is this:—If a lever, with equal arms, be acted on at its opposite ends by forces, in a given ratio to one another, and having their directions parallel to straight lines given in position, and if these forces be resolved each into two, one at right angles to the lever, and the other in the direction of it: in the case of equilibrium, the sum of the two forces, having the same direction with the lever, will be the greatest possible. This theorem, remarkable for its simplicity, and for illustrating the connection between the equilibrium of bodies, and certain problems concerning the maxima or minima of variable quantities, occurred when he was pursuing some of his inquiries concerning magnetism. He seems not to have been very fortunate, however, in his investigation, which is more complex than is necessary, as the proposition admits of a geometrical demonstration, remarkable for its simplicity.

AEROLITE, a term recently, but perhaps improperly, applied to those singular substances commonly called. The reader will find an interesting article upon this subject under the word in the body of the work; and we shall give such additions as may be necessary, under , in this Supplement. 

the article Aerostation in the Encyclopædia, the memorable invention of Balloons, the methods employed for constructing these aërial vehicles, with the remarkable circumstances attending their earlier ascents, are related at some length. But since that article was drawn up, several voyages have been performed through the atmosphere with more brilliant success, and often directed to the purposes of philosophical research. The various attempts at mounting into the air, and the progress of opinion among men respecting such a wonderful art, deserved likewise more notice, as interesting monuments at once of human ingenuity and of human weakness. The term Aerostation, first used, and signifying merely the weighing of air, might seem to refer simply to the buoyant property of balloons, and to preclude all discussion concerning the circumstances which determine their floating in any given stratum, or which regulate the force and celerity of their ascension, or of their subsequent descent. We prefer, as more correct and appropriate, the word Aeronautics, now generally adopted to express aërial navigation. Following out this more extended signification, we design at present to take a retrospect of the whole subject; to mark the progression of science; to detail more fully the steps by which Montgolfier arrived at this capital discovery; to explain the calculation of the ascent and stability of balloons; and, passing rapidly over the different aërial navigations related before, to select some of their more varied and striking features; and to conclude with the narrative of two magnificent ascents in the atmosphere lately made in France, and undertaken solely from philosophical views.

In every stage of society, men have eagerly sought, by the combination of superior skill and ingenuity, to attain those distinct advantages which nature hes conferred on the different tribes of animals, by endowing them with a peculiar structure and a peculiar force of organs. The rudest savage learns, from his very infancy, to imitate the swimming of a fish, and plays 1em