SPECIFIC GRAVITIES. 



18: 



two pistons, which is comparatively small. Another 

 is the smallness of the compass within which the whole 

 is comprised ; for a man might, with one not larger 

 than a tea-pot, standing before him on a table, cut 

 through a thick bar of iron with as much ease as he 

 could chip pasteboard with a pair of shears. 



SECTION III. 



SPECIFIC GRAVITIES. 



In connection with Hydrostatics, the subject of the 

 specific gravities of bodies is one of importance. The 

 specific gravity of a substance is its comparative 

 weight with some other substance, an equal bulk of 

 each being taken. Water is usually the standard for 

 comparison. 



To ascertain the specific gravity, weigh the body 

 both in and out of water, and observe the difference ; 

 then divide the whole weight by this difference, and 

 the quotient will be the specific gravity of the body. 

 For example, if a stone weighs 12 

 lbs. out of water and 7 lbs. in 

 water, divide 12 by 5, and the 

 quotient is 2.4, which shows that 

 the stone is 2^ times heavier than 

 water. Figure 157 shows the 

 mode of weighing the body in 

 water, by suspending it beneath 

 •"^ , a balance on a hair or thread. 



It was in a similar way that 



Instrument fr taking Specific i i • i . 



Grainttes. Archimcdcs succeeded in detect- 



ing the suspected fraud in the manufacture of the gold- 



