48 THE MECHANISM OF LIFE 



mixture of oxygen and hydrogen for an indefinite period of time, 

 nothing happening in it. But let a spark pass through the gases, 

 and they will combine together with an explosion and generation 

 of heat, and the potential energy which they contained trans- 

 forms into the kinetic form. Prior to the explosion the mixture 

 might be represented thus : 



Hg, Hg, O2, etc., 



the molecules of the gases (each of them consisting of two atoms 

 bound together) being apart from, and not influencing each other ; 

 but after the spark has fired the mixture we have 



H2O, H,0, etc., 



the molecules now occupying a different position relative to each 

 ' other. Thus chemical energy is energy of position. 



Now before the explosion the mixture of hydrogen and oxygen 

 possessed kinetic energy (as a mixture and apart altogether from 

 the chemical nature of its constituents). Each molecule was 

 moving with a certain velocity, and from the temperature and 

 pressure of the gas the average velocity of all the molecules can 

 be determined. The mixture can do mechanical work, for if it 

 were allowed to rush into a vacuum it could drive in a piston 

 just as steam drives in the piston in a cylinder. But as the 

 explosion occurs, the work that the gases can do is enormously 

 increased (thus the explosion can propel a projectile if it is fired 

 in a suitable vessel), and this energy that appears is the increased 

 kinetic energy of the molecules of steam at a very high tempera- 

 ture — that is, the latter are now moving with much greater 

 velocities than were the molecules of hydrogen and oxygen, and 

 so they exert a greater pressure. 



The energy therefore becomes manifest, or visible, in its 

 mechanical effects; but where was it before the explosion 

 occurred ? We cannot answer this question, and we assume 

 that it was not in the molecules of hydrogen and oxygen, but 

 was in the medium between them — that is, in the ether of space. 

 The hypothesis is one that does not lead us astray, and there- 

 fore we assume its validity or " truth." 



Available chemical energy, the energy of a weight raised above 

 the surface of the earth, and free to fall when it is released, and 

 that of a coiled spring — these are examples of potential energy 

 which transforms into kinetic energy, or the motion of bodies, 

 when a releasing transformation occurs. 



