114 SPECIFIC GRAVITY. 



same gravitation, in proportion to its quantity of 

 matter, as the lead which sinks to the bottom. The 

 absolute gravity of any one substance is exactly the 

 same as that of any other ; and the only variations 

 are, there being less or more of the substance in an 

 equal space, or substances being nearer to each 

 other or farther asunder. 



The variations of weight in an equal bulk, or of 

 bulk in an equal weight, of different kinds of matter, 

 are called their specific gravities, because they are 

 one of the means by which the species of matter are 

 known and distinguished from each other. The 

 specific gravity is known by weighing equal bulks, 

 or measuring equal weights ; and that which mea- 

 sures least when the weights are equal, and weighs 

 most when their bulks are equal, has the greater 

 specific gravity. It is of no consequence to which 

 of these methods singly we have recourse, or 

 whether we have recourse to both of them jointly 

 as we must have in all cases where the specimens 

 which we compare are neither of the same weight 

 nor of the same bulk. In those cases the common 

 mode of expression is, that the specific gravity is 

 as the weights directly, and as the bulks inversely 

 which means, that if both substances are weighed, 

 and both measured, by standards which are the same 

 as applied to both, then, if the weight of each be 

 multiplied by the bulk of the other, the products will 

 express the relation of the specific gravities. 



But the specific gravity of particular substances 

 is not, like the absolute gravity of one substance, 

 unalterable. The very notion of it is compound : 

 both weight and measure enter into it, and its value 

 is expressed by their product ; and the same product 

 may be obtained from any two numbers, if the one 

 be increased in the same proportion as the other is 

 diminished. Thus the number sixteen is four times 

 four, or two times eight, or one and one-third times 

 twelve, or one time sixteen, or one-half time thirty- 



