104- SPECIFIC GRAVITY. 



stance 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 mat- 

 ter, are called their specific gravities, because they 

 are one of the means by which the species of mat- 

 ter are known and distinguished from each other. 

 The specific gravity is known by weighing equal 

 bulks, or measuring equal weights ; and that which 

 measures 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 six- 

 teen is four times four, or two times eight, or one 

 and one-third times twelve, or one tune sixteen, 



