SPECIFIC GRAVITY of a body is the relation of its weight, compared with the weight of some other body of the same magnitude. A body immersed in a fluid will sink if its specific gravity be greater than that of the fluid ; but if it be less, the body will rise to the top, and will be only partly uncovered. If the specific gravity of the body and fluid are equal, then the body will remain at rest in any part of the fluid. If the body be heavier than the it loses as much of its weight when immersed as is equal in weight to a quantity of the fluid of the same bulk. If the specific gravity of the fluid be greater than that of the body, then the quantity of the fluid displaced by the part immersed is equal in weight to the weight of the whole body. There fore the specific gravity of the fluid is to that of the body as the whole magnitude of the body is to the part immersed. The
specific gravities of solids are as their parts immersed in the same fluid. The specific gravities of fluids are as the weights lost by the same immersed body.
To form a table of the specific gravities of various substances, it is necessary to select one as the standard of comparison : in practice, pure water is always chosen as the starting-point for solids and and pure atmospheric air for gasses, the number 1 (1.000) expressing the specific gravities. The formation of two series is considered to be more convenient than the comparison of all bodies by one stand ard, on account of the complexity of the numbers which would result.
The following is a table of the spec fie gravities of a number of substances : all those solids which are capable of absorb ing moisture are assumed to be dry.