CHAPTER VIII 



ARCHIMEDES' PRINCIPLE. WATER-PRESSURE 

 AND WATER-WORKS 



Archimedes (287-212 B.C.) was the greatest of the 

 ancient mathematicians. He lived in Syracuse on the 

 island of Sicily. The king of Syracuse in Archimedes' 

 time once ordered of a goldsmith a crown of pure gold. 

 It was delivered to him. It looked like pure gold and it 

 had the proper weight. Still the king had reason to sus- 

 pect that the goldsmith had cheated by melting up silver 

 along with the gold. He asked Archimedes to discover 

 a method of proving the fraud. A modern chemist could 

 have solved the problem in a minute, but chemistry in 

 those days was unknown. So the mathematician put 

 his wits to work. He was sorely puzzled. One day, while 

 in the public bath, he noticed that the part of his body 

 under the water was much lighter (more buoyant) than the 

 part above it. He got to thinking about this. Suddenly 

 he jumped from the bath like a crazy man (so the story 

 goes), rushed into the street without waiting to dress, and 

 ran home shouting "Eureka! Eureka!" which means "I 

 have found it." 



' Now what had occurred to Archimedes was this: He 

 knew that gold and silver are different as to their buoyancy 

 in water, or, as we say now, as to the specific gravity. So 

 taking a weight of gold equal to the weight of the crown; 

 and comparing it with the crown as to buoyancy, he could 

 prove whether the crown was pure gold or not. 

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