SCIENCE OF THE GREEKS. 



PT. I. 



as I have explained it ; but as you may perhaps be puzzled 

 to see how it can have anything to do with weight, it will 

 be well to try to master the following explanation of Fig. i, 

 which shows how specific gravity is measured. You must 

 begin by remembering that the crown, the gold lump, and 

 the silver lump, when weighed in the air, will all pull the 

 marker of the spring balances A, B, c, down to 1 9 ; that is, 



FIG. i. 



Diagram showing the difference of specific gravity between equal weights of gold, 



silver, and mixed metal. 

 ABC, Spring balances, d, Gold ball weighing 19 02. e, Silver ball weighing 19 oz. 



/, Crown of mixed metal weighing 19 oz. 



they will all weigh 19 ounces. But when they are immersed 

 in water they will no longer weigh the same, because the 

 water round them buoys them up just as much as it would 

 buoy up the quantity of water which they displace. 



