GRAVITY, specific. Boyle is among the first of our philosophers, who suggested the advantage that chemistry and minera logy might derive from an attention to the specific gravities of bodies. Much advantage may indeed be derived from this property in the general determina tion of the classes of minerals, and the purity of some metallic bodies ; and it is very probable, that an attention to the specific gravities, capacities for heat, fu sibilities, volatilities, laws of crystalliza tion, elasticity, hardness, tenacity, mallea bility, and some other obvious specific properties of bodies, may produce a more intimate acquaintance with the mutual ac tions of their particles, than any we have hitherto acquired.
Annexed to this article is a table of spe cific gravities, from various authors. It appeared useless to carry it to more than four places of figures, as the temperatures are not noted ; and the various specimens of the same substance often differ in the third figure. Besides this, it is remarked by Nicholson, in his " Chemical Diction. ary," that the fifth figure changes in wa. ter at every three degrees of Fahrenheit's thermometer ; that lead, tin, and proba bly all other metals, though cast out of the same fusion, will vary in their speci fic gravities in the third figure, from cir cumstances not yet determined, but most likely from the cooling, as is seen in the hardening of steel ; that salts, and other artificial preparations, retain more or less of the solvent they were separat ed from, according to the temperature at which the crystallization was effected ; and that all parts of organized substances not only differ, according to the place of their production, their age, and other cir cumstances, but likewise from their dry ness, moisture, and manner of preserva tion.
The specific gravity of solids is deter mined by weighing them, first in air, and then in water. The loss of weight, aris ing from the action of the water, is equal to that of a mass of the fluid possessing the same dimensions as the solid itself.
Whence it is easy to construct a general table of specific gravities, by reducing the proportion of the absolute weight to the loss sustained by immersion, into terms of which that expressing water shall be unity. If the solid be so light as to float upon water, it is convenient to at tach to it a heavier body sufficient to cause it to sink, but the weight of which in wa ter must be added in computing the loss. The specific gravity of fluids is ascertain ed by weighing a known body immersed in them. For the loss by immersion will accurately show the weight of the same bulk of the fluid ; and, consequently, the proportion of these several quantities to the loss the same solid sustained in water being reduced, as in the other case, to the common standard of unity, will exhibit the specific gravity. Other methods are likewise used in experiments with fluids. Thus equal bulks of different fluids may be weighed by filling a small bottle with a ground stopper with each respectively, and from their several weights the weight of the bottle and stopper must be deduct ed. Or, otherwise, the instrument called the hydrometer may be used. See lly DROMETER. This possesses the advantage of portability, speed, and a degree of ac curacy, not easily obtained by the use of ordinary balances.
Gaavrrv, in music, is the modifica tion of any sound, by which it becomes deep or low in respect of some other sound. The gravity of sounds depends on the thickness and distension of the chords, or the length and diameter of the pipes, and in general on the mass, extent, and tension of the sonorous bodies. The larger and more lax the bodies, the slow er will be the vibrations and the graver the sounds.