AIR AND WATER AS SERVANTS OF MAN 115 



called in the Greek scientist, Archimedes, and assigned him the 

 task of determining whether the crown was pure gold. The king 

 required that he solve the problem within a specified time or 

 lose his life. Archimedes, therefore, went to the task with much 

 energy. He knew, of course, that gold is much heavier than 

 silver, and if he could but know the volume of the crown, knowing 

 the weight of gold, he could tell how much it should weigh. His 

 chief problem, therefore, was to find the volume of the crown. 

 He could not, of course, pound it into a lump that could be 

 measured, and so he pondered intently on the task of measuring 

 the volume of the crown. The story relates that he went to take 

 his bath and rather absent-mindedly filled the tub too full, and 

 when he got into the tub the water overflowed. Archimedes 

 saw at once that a body that is immersed in water displaces 

 its own volume and herein was the means of determining the 

 volume of the crown. He was so excited that he ran home from 

 the bath, crying, "Eureka! Eureka! I have found it!" much to 

 the astonishment of the citizens, for he had not waited to put 

 on his clothes. 



Now cut out another block of plasticine the same size as the 

 one used above, and weigh it carefully. Again fasten it to the 

 thread and fasten the thread to the pan of the scales or the hook 

 of a spring scale. Immerse the plasticine in water as before and 

 note what it weighs as it hangs in the water. Remove the 

 plasticine and exactly balance a glass graduate on the scales, 

 then add 5 cubic centimeters of water. It will be found that 

 the water weighs 5 grams and also that the difference in the 

 weight of the plasticine in air and in water is 5 grams. In 

 other words, the plasticine immersed in water loses as much 

 weight as the weight of the water which it displaces. 



The reason for this is perfectly evident when we consider the 

 block of plasticine immersed vertically in the water. The 

 pressure on opposite sides of the block will evidently be identical 

 since the opposite sides are exactly of the same area and are at 

 the same depth in the water. The downward pressure on the 



