a8 How to find Specific Gravity. [Book L 



it amounts to fifteen ounces, and on weighing it in 

 water it appears that it has loft two ounces of its 

 weight. The fpecific gravity of tin is therefore to 

 that of water as 15 to 2, or as 7 { to r, confequently 

 the comparative gravities of the two metals are 117 

 to 7 I *. 



In the common tables of fpecific gravities, the 

 weight of water is eftimated at i , and that of other 

 fubftances is exhibited in the fame ratio. To deter- 

 termine therefore the fpecific gravity of any fubftance 

 heavier than water, weigh any given quantity of that 

 fubftance in air in a common balance, and afterwards 

 weigh it in water, carefully noting its lofs of weight ; 

 divide the whole abfolute gravity, or weight in air of 

 the fubftance, by its lofs of weight in water, and you 

 will have its fpecific gravity. 



IV. The attraction of MAGNETISM only differs from 

 that of gravity in its operations being limited to par- 

 ticular fubftances. The magnet is an ore of iron, and 

 its property of attracting certain portions of that me- 

 tal at moderate diftances is well known. Like the at- 

 traction of gravitation, that of magnetifm bears a pro- 

 portion to the diftance, and probably to the quantity 

 of matter (I fhouki fay of magnetic matter) in the at- 

 tracting bodies. But the properties of the magnet are 

 Ib curious and important in nature, that they well de- 

 ierve a diftinct chapter. 



V. The attraction of ELECTRICITY is alfo analogous 

 to that of gravity in the property of acting upon bo- 

 dies at a certain diftance ; but it differs from it in its 

 operation being confined to a particular ftate of thofc 

 bjdies, that is, when excited by friction. But this pe- 



* Nicholfon's Philofophy, V. ii. p. u. 



culiar 



