HYDROSTATICS. 175 



When the body is heavier than water, this correction 

 is subtractive ; when lighter, it is additive. 



The manner of finding the specific gravity of air will 

 be afterwards explained. 



258. If B be the bulk of any body in cubic 

 inches English, W its weight in grains, and 

 S its specific gravity, that of water being 1 ; 

 W 



T> -- . 



(252.576) S " 



This theorem is founded on an experiment of Sir G. 

 SHUCKBOROUGH'S (Phil. Trans. 1798), by which 

 the weight of a cubic inch of distilled water, of the 

 temperature 66, was found to be 252.422 grains, 

 which, reduced to the temperature 60, is 252.576. 

 CAVALLO, vol. n. p. 98. 



The logarithm of 252.576 is 2.4023921. 



If W is expressed in Ib. Troy, it must be multiplied 

 by 5760 ; if in Ib. avoirdupois, by 7002. If B is 

 required in cubic feet, its value thus found must be 

 divided by 1728. 



SECT. 



