ARCHIMEMES, the PRINCIPLE OF, is one of the most important in the science of Hydrostatics, and is so called because the discovery of it is generally ascribed to the Syracusan philosopher. It may be thus stated: A body when immersed in a fluid loses exactly as much of its weight as is equal to the weight of the fluid it displaces; or: A fluid sustains as much of the weight of a body immersed in it as is equal to the weight of the fluid displaced by it. It is proved experimentally in the following way. A delicate balance is so arranged that two brass cylinders, A and B, may be suspended from one of the scale-pans, the one under the other. The lower cylinder, B, is solid, or closed all round, and fits accurately into the upper cylinder, A, which is hollow. When the two cylinders are placed under the one scale, pan-weights are placed upon the other until perfect equilibrium is obtained. The cylinder B is now immersed in water, and in con sequence of the buoyant tendency of the Water exerted upon it, the equilibrium is destroyed; but it may be completely restored by filling the hollow cylinder, A, with water. The amount of weight which B has lost by being placed in the water, is thus found to be exactly the same as the weight of a quantity of water equal to its own bulk, or which is the same thing, to the quantity of water displaced by it. When bodies
lighter than water are wholly immersed in it, they displace an amount of water of greater weight than their own, so that if left free to adjust themselves, they swim on the surface, only as much of their bulk being submerged as will displace a quantity of water weighing the same as themselves. Accordingly, while bodies heavier than water displace, when put into it, their own bulk, bodies lighter than water displace, when allowed to float ou the surface, their own weight of the fluid. Bodies of the same weight as water, according to the principle of Archimedes, have no tendency to rise or sink in it, for the water displaced by them weighs precisely the same as they do. The pretty scientific toy called the Cartesian diver is intended to illustrate this. Although the principle of Archimedes is immersed established with reference to water, its applica tion extends equally to bodies mmersed in air or any other fluid.