CH. in. ARCHIMEDES SPECIFIC GRAVITY. 2 $ 



Now, the gold takes the place of as much water as would 

 weigh one ounce if you could take it out and weigh it in the 

 air. So it is buoyed up one ounce by the water round it, 

 and accordingly you see it only pulls the marker down 1 8 

 ounces instead of 19. But the silver, although it weighs 

 the same, is larger, and takes the place of nearly two ounces 

 of water, therefore it is buoyed up nearly two ounces, and 

 only pulls the marker down to 17. Now, as the crown 

 weighs the same as either of the two lumps, its shape is of 

 no consequence ; if it was made all of gold it would take 

 as much room, and be buoyed up as much as the gold. If 

 it was all silver it would be buoyed up as much as the silver, 

 and therefore, as it pulls the marker down half-way between 

 1 7 and 1 8 ounces, it must be half gold and half silver. 



In this way Archimedes showed how we can learn the 

 weight of any solid compared to an equal bulk of water, 

 and this is called the ' specific gravity ' of the substance. 



He also invented a screw for pumping up water, which 

 is still called the ' screw of Archimedes.' 



Archimedes was unfortunately killed in the city of Syra- 

 cuse when it was besieged by the Romans during the second 

 Punic war. The Roman general Marcellus had given 

 special orders that his life should be spared ; but he was so 

 deeply engaged in solving a problem that he heard nothing 

 of the din of war around him, and a common soldier not 

 being able to get any answer from him, killed him without 

 knowing who he was. 



