64 ELEMENTARY SCIENCE 



Whether Archimedes discovered the goldsmith to be 

 a fraud or not is not important. He had made a discovery 

 far more important than that. He had discovered what 

 is known even to-day as Archimedes' principle: the prin- 

 ciple that a body immersed in a liquid is buoyed up by a force 

 equal to the weight of the liquid that it displaces. 



If the body weighs more than the amount of liquid dis- 

 placed, it will sink; if less, it will float. A floating body 

 sinks to such depth in the liquid that the weight of the 

 liquid displaced equals the weight of the body. This ap- 

 plication of Archimedes' principle you can easily prove. 

 Take a piece of wood coated with paraffin to prevent its 

 absorption of water. Fill a pitcher with water until it 

 overflows at the spout. Then float the wood in this water 

 and catch all that runs out of the spout. The water thus 

 obtained and the piece of wood should weigh the same. 

 Try the same thing with a piece of ice, making allowance 

 for the melting of the ice. Is it true that seven times as 

 much of an iceberg is under water as above it ? 



By means of Archimedes' principle we may also com- 

 pute the volume of solid objects of any shape. Weigh 

 the object in air, and then weigh it under water. The 

 difference in the two weights represents the weight of the 

 water displaced. Suppose this difference be ten grams. 

 We know that ten grams of water by weight is ten cubic 

 centimeters of water by volume. We also know that the 

 volume of water displaced is identical with the volume of 

 the object submerged. Therefore, the volume of the object 

 is ten cubic centimeters. In other words, the difference in 

 grams between the weight of an object in air and its weight 

 in water is equal to the wlume of that object in cubic centi- 

 meters. 



