USES OF WATER 117 



ing the crown. While in his bath one day, he happened 

 to notice the loss of weight of his own body, and the whole 

 principle suddenly occurred to him that a body immersed 

 in water must lose a weight equal to the weight of- the 

 water displaced. This discovery made his problem quite 

 simple, since gold has a volume which in proportion to its 

 weight is smaller than that of any other metal except 

 platinum. Archimedes determined, therefore, that the 

 crown was made of pure gold, since an equal volume of 

 any other metal would lose a greater proportion of its 

 weight when immersed in water. 



Most of us are acquainted with this principle long 

 before any statement of it is made. We know that many 

 objects float, and it is quite evident that if an object such 

 as a piece of wood or a boat floats, the upward force of 

 the water must be equal to the weight of the body. A 

 piece of iron will sink in water, but if mercury is used, the 

 iron will float as cork on water. An iron vessel will float 

 on water because the vessel is so shaped that it displaces 

 more water than the volume of the metal used in its con- 

 struction. As a vessel is loaded, it sinks deeper and 

 deeper into the water, but only sinks deep enough to dis- 

 place an amount of water, equal in weight to the weight 

 of the ship and its cargo. 



Submarines. A submarine boat is so constructed that 

 no water can enter it even if it is completely submerged, 

 excepting as permitted to enter by the occupants of the 

 boat. If the boat is to dive, water is admitted into 

 special compartments until the weight of the boat slightly 

 exceeds the weight of the water it displaces. If the weight 

 of the boat exactly equals the weight of the water it dis- 

 places, it will remain stationary at any depth below the 

 surface. When the boat is to rise to the surface, water 



