152 THE REALITIES OF MODERN SCIENCE 



to the earth more of his momentum than will the lighter 

 man. 



Newton demonstrated the equality of the components 

 of a stress as follows. He floated two bowls in a large 

 vessel of water. In one was a magnet and in the other 

 a piece of iron. The magnet attracts the iron. The 

 iron reacts on the magnet. The two bowls, therefore, 

 float together. If, however, the action is greater than 

 the reaction the magnet will keep pulling the iron along 

 and the combination will move Conversely, if the 

 reaction is greater the two bowls will move in the op- 

 posite direction. Since neither bowl propels the other, 

 action and reaction must be equal and opposite. 



If one could propel the other there would be a viola- 

 tion of the principle of the conservation of energy. 

 We could arrange a circular water path and allow the 

 magnet to propel the iron around this path. Connect- 

 ing the rim of a wheel to the magnet, we could obtain 

 useful work. The result would be a " perpetual mo- 

 tion" machine. 



Perpetual motion machines are those which will 

 do useful work without requiring that at least an 

 equal amount of work shall be done upon them, that 

 is, machines which will create energy. In the early 

 days of experimental science there were many seekers 

 after a machine of this type, and ingenious were the 

 fallacies by which they persuaded themselves that their 

 designs followed known laws of physical science. While 

 the search was fruitless, the experimentation served 

 some purpose in advancing science just as did the 

 equally fruitless search of the alchemists. 



To that master philosopher, Newton, such quests 



