24 



SCIENCE OF THE GREEKS. 



PT. r. 



gravity of different substances, that is, the weight of any 

 particular substance compared to an equal bulk of water. 



It will be quite sufficient if you remember the experiment 

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

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

 if you wish, try to master the following explanation of Fig. i, 



Fig. I. 



Dia^am showing the difference of specific gravity between equal weights of gold, 



silver, and mixed metal. 

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



f. Crown of mixed metal weighing 19 oz. 



which shows how specific gravity is measured. You must 

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

 silver ball, when weighed in the air, will all pull the marker of 

 the spring balances a, b, c, down to 1 9 ; that is, they will all 

 weigh 19 ounces. But when they are immersed in water they 



