360 THE PHILOSOPHY OF BIOLOGY 



were dissociated by the energy of the electric current 

 are different things from the atoms of hydrogen and 

 oxygen which are combined together to form the mole- 

 cules of water. Their state when the gases are in the 

 elementary condition, or are " free," is that of mole- 

 cules moving rapidly and incessantly, rebounding from 

 each other after colliding with each other : they possess 

 energy of position — potential energy — because they are 

 separate from each other. If they " combine," as when 

 a minute electric spark explodes the mixture of gases, 

 they tractate together, and remain in proximity to each 

 other, becoming molecules of water. The energy which 

 became potential in the gaseous mixture, when the 

 electric energy of the current seemed to disappear, now 

 appears as the heat generated by the combustion, that 

 is, as the greatly increased kinetic energy of the mole- 

 cules of the gas (steam) which takes the place of the 

 mixture of hydrogen and oxygen. Previous to the 

 explosion this gas was a mixture of molecules of 

 hydrogen and oxygen (2H2+2O) at the ordinary 

 temperature, but after the explosion it consists of a 

 smaller number of molecules at a very much higher 

 temperature. 



What is " energy of position " ? The golf ball at 

 the bottom of the hill was at a distance of R feet from 

 the centre of the earth, but at the top of the hill it is at 

 a distance of 2? +100 feet from the centre of the earth. 

 In the first case it was free to fall R feet, but in the 

 second case it is free to fall R + 100 feet. The atoms 

 of the constituent molecules of water occupy the 

 position H - O - H, the bonds ( - ) indicating that 

 the atoms are very close together; but when the 

 water is decomposed by an electric current, the 

 atoms occupy the positions O - O-f H - H+H - H, 

 the (+) indicating that the atoms are relatively 



