Chap. 2.] relative tofy'rific Gravity. 425 



Ninthly, the fpecific gravity of a folid is to that of 

 a fluid heavier than itfelf, and upon which it will fwim, 

 as the bulk of the immerfed part is to the bulk of the 

 whole body. So that if the magnitude or bulk of the 

 immerfed part is to the magnitude of the whole body 

 as two or three, the fpecific gravity of the folid is to 

 that of the fluid as two is to three. 



Tenthly, the weight and the magnitude of a body, 

 and alfo the weight of a fluid fpecifically heavier than 

 the body, being given, fuppofe it is required to find 

 the force requifite to keep that body entirely immerfed 

 in the fluid. As this force is equal to the fpecific 

 weight of the fluid, find, by means of the given bulk 

 of the folid, and the known weight of a cubic foot of 

 the fluid, by the rule of three, the weight of a bulk of 

 the fluid equal to the bulk of the folid. Subftraft from 

 this weigh:, the weight of the folid, and the remainder 

 will be the force required. For example, fuppofe it 

 was required to find the force neceflfary to retain under 

 water a folid of eight cubic feet in contents, and of 

 four hundred pounds weight. Since a cubic foot of 

 water weighs about feventy pounds, the weight of 

 eight cubic feet of water is five hundred and fixty 

 pounds ; then if four hundred pounds are lubftracted, 

 the one hundred and fixty remainder, is the force ne- 

 cefTary to keep the folid immerfed in the water, and to 

 prevent it from rifing to the furface. 



Eleventhly, the weight of a body fpecifically heavier 

 than a fluid, and the weight of that fluid fpecificaily 

 lighter, being given, fuppofe it is required to deter- 

 mine the cavity which that body mould have, in order 

 that it may fvvim upon the fluid. 



The weight of a cubic foot of the fluid being given, 

 ths bulk of the portion of the fluid equal in weight to 

 that of the body, is found by the rule of three. If then 



the 



