OF THE SPECIFIC GRAVITIES OF BODIES. 179 



again, and goes down empty, until it comes to the water 

 at A, where it is filled as before. On each bucket is a 

 spring r, which, going over the top or crown of the bar 

 m (fixed to the trough A/ ), raises the bottom of the 

 bucket above the level of its mouth, and so causes it to 

 empty all its water into the trough. 



Sometimes this wheel is made to raise water no 

 higher than its axle ; and then, instead of buckets hung 

 upon it, its spokes C, d, e,f, g, h, are made of a bent 

 form, and hollow within ; these hollows opening into 

 the holes C, D, E, F, in the outside of the wheel, and 

 also into those at O in the box X upon the axle. So 

 that, as the holes C, D, &c. dip into the water, it runs 

 into them ; and as the wheel turns, the water rises in 

 the hollow spokes, c, d, &c. and runs out in a stream 

 P from the holes at O, and falls into the trough Q, from 

 whence it is conveyed by pipes. And this is a very 

 easy way of raising water, because the engine requires 

 neither men nor horses to turn it. 



The art of weighing different bodies in water, and of the 

 thereby finding their specific gravities, or weights, bulk spe ^^ eis 

 for bulk, was invented by ARCHIMEDES ; of which we of bodies, 

 have the following account : 



Hiero, king of Syracuse, having employed a gold- 

 smith to make a crown, and given him a mass of pun, 

 gold for that purpose, suspected that the workman 

 had kept back part of the gold for his own use, and 

 made up the weight by alloying the crown with copper. 

 But the king, not knowing how to find out the truth of 

 that matter, referred it to Archimedes ; who, having 

 studkd a long time in vain, found it out at last by 

 chance. For, going into a bathing tub of water, and 

 observing that he thereby raised the water higher in the 

 tub than it was before, he concluded instantly that he 

 had raised it just as high as any thing else could have 

 done, that was exactly of his bulk : and considering 

 N 2 



