2nd. Consequent on the velocity of the explosive fluids is the resistance of that aëriform fluid filling all space. It has been calculated that in a vacuum, matter in motion would be a long time in coming to rest; and very providentially it is that nature in her grand arrangements has made one element to control another. In no other portion of nature’s work has anything more wonderful than atmospheric air been produced; its action on the velocity of projectiles is of so extensive a nature, that without clearly understanding that action, the science of gunnery never can be thoroughly acquired. The resistance of the atmosphere is in proportion to the velocity of the attempt to displace it; the higher that velocity becomes, the greater is the resistance. This is shown by the actions of all the fulminates. A quantity of the fulminate of silver exploded on a copper plate will perforate that plate, or, if fired upon a piece of wood, will bury itself in that substance, splintering it in proportion to the quantity. Now, ordinary gunpowder has no such effect as this, because, though it may produce the same amount of expansive gas, it produces it at one-fourth the velocity of the fulminates: the air is driven back upon itself so gradually as to offer no very important resistance; but the action of the fulminates is so rapid and so violent that the high elasticity of the air has not time to yield, and the force is driven into the apparently more solid material, the copper or the wood. The mode in which atmospheric resistance mostly interferes with projectile force is owing to the columnar form it assumes in the tubes of all descriptions of gunnery. If the velocity of gunpowder be as great as we suppose it to be, the displacement of a column of air must be effected by driving the whole column in a gun-barrel of many inches, into a column probably less than half an inch in height; or, if the length of the tube from the starting of the charge to the muzzle be 38 inches, then will the displacement require a force capable of condensing thirty-eight atmospheres into one, or something like 570 lbs.; without estimating the lateral pressure of that column on the sides of the gun-barrel, which may be safely estimated at one-half more. It may be supposed that the column would be partially in motion for a greater distance than half an inch in front of the projectile; but this is disproved by the fact that time is essential to put aëriform matter in motion, and naturally it never does so at a greater velocity than it is familiarly known to do in the shape of winds: but the fact is better illustrated by the frequent bursting of barrels near the muzzle, caused by a piece of snow or clay, a piece of paper or wadding. Were a current established around this projection it would pass on, but the air strikes these light obstructions when in a high state of condensation, amounting to many atmospheres in one: so many as to be nearly equal to a solid