42 THE REALITIES OF MODERN SCIENCE 



force equal to the weight of the fluid they displace. 

 Of course, if a body is not entirely immersed it is 

 buoyed up with a force equal to the weight of the fluid 

 which the immersed portion of the body displaces. We 

 speak of ships to-day in tons displacement, stating 

 the weight of the water displaced and hence a measure 

 of the total weight which the ship and cargo may have 

 if its tendency to sink is to be neutralized by the 

 buoyancy of the water. 



The story of how Archimedes (287-212 B.C.) hap- 

 pened to arrive at his law is told by Vitruvius, the 

 Roman engineer and architect who wrote about the 

 time of Christ. " Though Archimedes discovered 

 many curious matters that evidenced great intelli- 

 gence, that which I am about to mention is the most 

 extraordinary. Hiero, when he obtained the regal 

 power of Syracuse, having, on the fortunate turn of 

 his affairs, decreed to be placed in a certain temple a 

 votive crown of gold to the immortal gods, commanded 

 it to be made of great value, and assigned to the manu- 

 facturer for this purpose an appropriate weight of 

 the metal. The latter in due time presented the work 

 to the king. It was beautifully wrought and the weight 

 appeared to correspond to that of the gold which had 

 been assigned for it. But a report was circulated that 

 some of the gold had been abstracted and that the de- 

 ficiency thus caused had been supplied by silver. Hiero 

 was indignant at the fraud, and unacquainted with a 

 method by which the theft might be detected, requested 

 Archimedes to give it his attention. While charged 

 with this commission Archimedes went by chance 

 to a bath. On getting into the water he noticed that 



