AIGLETS is the French name for what in England are called lags, viz., the metal sheaths at the end of laces or points. These points are now out of date; they were ties or bows, adorned at the ends with aiglets, and were used instead of buttons for fastening dresses. They were, in the lath and 17th centuries, not used merely for service, as the modern tag, but were profusely employed as orna ments, glittering like spangles.
In some of the silk-nfills of Derby, tags for silk boot-laces are made in a curious manner. A little boy sits before a kind of cutting-ma chine, with which he cuts a strip of sheet-brass into small pieces, each large enough for one tag ; the piece is at the same time bent into a kind of semi-cylindrical form. The pieces are then taken up by another boy, and dropped one by one into a recess in another machine; and the end of a silk-lace being laid in the hollow of a tag, a lever is brought down with the left hand, by which the tag is made to embrace the lace firmly, enclosing it all round. These processes are conducted with astonish ing rapidity : the fingers of the two boys moving almost as fast as the eye can follow them. AIR, is the material of our atmosphere, though in the last century the name was ap plied to gases of most kinds as fast as they were discovered. The air which envelops the globe is a mixture (not a chemical compound) of oxygen and nitrogen, with a very small proportion of carbonic acid, and water in the state of vapour. The two last are considered as accidental ingredients, and not constituent parts ; as well on account of the smallness of their quantity, as because they occur in dif ferent proportions at different times. Esti mated by weight, air is found (nearly, but not with strict accuracy) to consist of one atom or equivalent of oxygen to two of nitrogen ; or, estimated by volume, the oxygen is to the ni trogen in the ratio of one to four. The car bonic acid and aqueous vapour, taken together, are not more than one fiftieth of the whole weight. A thousand cubic inches of dry air, the barometer standing at 30 inches, and Fahrenheit's thermometer at weigh about 310 grains. The same bulk of water, at the
same pressure and temperature, weighs 252,525 grains, or more than 800 times that of air. • The air, in common with all other bodies, has weight. This is proved by weighing a bottle which contains air in a very delicate ba lance, and then by repeating the process after the air has been exhausted from the bottle by the air-pump. From this we are immediately led to conclude that, like all other heavy fluids, air exercises pressure upon all substances which are in contact with it,—a truth that was very little suspected in ancient times. The density of the air depends upon, and is a consequence of, the pressure of the superincumbent atmos phere; or the air is an elastic fluid ; that is, its bulk increases, and its density diminishes, whenever the exterior pressure is wholly or partially removed. Let a loose bladder, tied at the mouth, and not so full of air as to be distended, be placed under the receiver of an air-pump, so that the air which presses the outside of the bladder can be exhausted ; the interior air will expand so soon as the exhaus tion begins, will presently distend the bladder to its fullest dimensions, and in some cases will even burst it. On the re-admission of the air into the space surrounding the bladder, the latter will gradually resume its former dimen sions, and its withered or flaccid appearance. As we ascend the atmosphere, the superin cumbent column of air becomes of less weight, and the density becomes less; that is, a cubic foot at the height of (say) 1000 feet above the ground is not so heavy, or does not contain so much air, as a enbie foot at the surface of the earth. The pressure and density of the air are regulated by the following law : at the same temperature, the elastic forces of two portions of air (Cr, which is the same thing, the weights of mercury they will balance) are in direct proportion to the densities, or in inverse pro portion to the spaces, occupied by these por tions. The human body would be crushed by the pressure of the air on it, were there not a counter pressure from within.