HYDROSTATICS. 11? 



thus continues to go downwards, until stopped by 

 an impervious bed, as rock or clay, and following 

 the course of this bed, it breaks out on the surface, 

 at the first place where the soil permits its exit. 

 The existence of springs, therefore, always requires 

 that there shall be ground on a higher level, 

 together with an alternation of hard and soft 

 beds. 



OF SPECIFIC GRAVITIES. 



By the specific gravities of bodies is meant the 

 relative weights which equal bulks of different bo- 

 dies have to each other. It is usual to compare 

 them with that of water, as it is by weighing bodies 

 in water that their specific gravities are found. 



The method of ascertaining the specific gravities 

 of bodies was invented by Archimedes upon the 

 following occasion. 



Hiero, king of Syracuse, having given a quantity 

 of pure gold to a workman to make a crown of, sus- 

 pected that he had kept part of the gold, and adul- 

 terated the crown with a baser metal. He applied 

 to Archimedes to discover the fraud, who having 

 long studied it in vain, accidentally hit upon a 

 method of ascertaining it. Going one day into a 

 bath, he took notice that the water rose in it, and 

 immediately reflected, that any body of an equal 

 bulk with himself would have raised the water just 

 as much ; though a body of equal weight, but not 

 of equal bulk, would not raise it so much. From 

 this idea, he conceived a mode of rinding out what 

 lie so much wished, and was so transported with 

 joy, that he ran out of the bath, naked as he was, 

 crying, "I have found it, 1 have found it!" 



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