INTRODUCTION. 13 



29. If in two bodies of which the bulks are B 

 and B', and the weights W and W, the weights 



W B' 



be proportional to the bulks, or - m ^-, the 



space occupied by the pores of these bodies bears 

 the same proportion to that which is filled by solid 

 matter. 



Bodies of this kind are said to have the same den- 

 sity. 



30. The weight of a body divided by its bulk, 



W 



or ip is called the specific gravity of the body. 



a. The weight of a body, in strictness, cannot be di- 

 vided by its bulk, the two quantities being dissimi- 

 lar, and incapable of comparison. But if we ex- 

 press the bulk of all bodies numerically, by refer- 

 ring them to the same unit, a cubic inch for ex- 

 ample; and the weight of all bodies, by referring 

 them to a similar unit, the weight of a cubic inch 

 of water, any number in the first series may be di- 

 vided by the corresponding number in the second : 

 the quotient will be the specific gravity of the body 

 to which the numbers belong. 



Hence the specific gravity multiplied by the bulk, 

 gives the weight; or if S is the specific gravity r 

 B x S = W. 



31. A 



