MAGNETISM. 135 



into relation with hydrogen. Hydrogen has it when brought 

 into relation with oxygen. Mixed oxygen and hydrogen have 

 an enormous power, if ignited when the surrounding media 

 are at a certain temperature, but if these are above the tem- 

 perature at which decomposition of water by heat takes place, 

 the potential energy of the gases in relation to each other is 

 nil] they cannot combine by the application of heat, and they 

 must be chilled to evolve active force. 



Dr. Odling has shown that these and other substances on 

 entering into combination necessarily evolve heat, and it seems 

 probable that, if the heat surrounding them be greater than 

 that evolved by their combination, the heat they would evolve 

 cannot be conveyed away, and consequently that they would 

 not combine. 



A stone on a hill has a potential energy with reference to 

 the valley beneath, and when it has reached that it has a 

 potential energy with reference to the bottom of a mine. 



Every particle of matter has in it a locked up or potential 

 energy when it is in equilibrium, but active when the equili- 

 brium is disturbed. It is capable as the case may be of heat- 

 ing, of cooling, of oxidating, of deoxidating, of evaporating, 

 of condensing, &c., according to the state of surrounding bodies. 



A weight raised from the earth not only has the potential 

 energy of its tendency to fall, but, as I have before observed, 

 changes the centre of gravity of the earth (which may be said 

 to have thus acquired new potential energy), and alters its 

 relation to the solar and other systems. The whole universe 

 has thus acquired new potential energy when a stone has 

 been lifted by a crane and placed on a wall. Could we not 

 hope to arrive at more accurate scientific ideas if we expressed 

 ourselves in terms of actual motion and discarded latent or 

 non-acting force ? Thus, if by raising a stone the centre of 

 gravity of the earth be changed, the sun and planets, &c. are 

 affected ; so that when we produce what is called a state of 

 potential energy, we are actually eliminating dynamic force 

 from other bodies. 



Were the state of things contemplated by Sir W. Thomson 

 (p. 67) to be the ultimate result of all other energies being 

 resolved into uniform diffused heat, the total energy in the 



