56 CORRELATION OF PHYSICAL FORCES. 



posed to a temperature of about 800, they combine and form 

 water ; heat therefore appears to act differently upon these 

 elements according to its intensity, in one case producing 

 composition, in the other decomposition. No satisfactory 

 means of reconciling this apparent anomaly have been pointed 

 out : the best approximation to a theory which I can frame 13 

 by assuming that the constituent molecules of water are, be 

 low a certain temperature, in a state of stable equilibrium ; 

 that the molecules of mixed or oxyhydrogen gas are, above a 

 certain temperature, also in a state of stable equilibrium, but 

 of an opposite character ; while below this latter tempera 

 ture the molecules of mixed gas are in a state of unstable 

 equilibrium, somewhat similar to that of the fulminates or 

 similar bodies, in which a slight derangement subverts the 

 nicely-balanced forces. 



If, for instance, we suppose four molecules, A, B, C, D, 

 to be in a balanced state of equilibrium between attracting 

 and repelling forces, the application of a repulsive force be 

 tween B and C, though it may still farther separate B and C, 

 will approximate B to A and C to D, and may bring them 

 respectively within the range of attractive force ; or, sup 

 posing the repulsive force to be in the centre of an indefinite 

 sphere of particles, all. these, excepting those immediately 

 acted on by the force, will be approximated, and having from 

 attraction assumed a state of stable equilibrium, they will re 

 tain this, because the repulsive force divided by the mass is 

 not capable of overcoming it. But if the repulsive force be 

 increased in quantity and of sufficient intensity, then the at 

 tractive force of all the molecules may be overcome, and de 

 composition ensue. Thus, water or steam below a certain 

 temperature, and mixed gas above a certain temperature, 

 may be supposed to be in a state of stable equilibrium, whilst 

 below this limiting temperature, the equilibrium of oxyhy- 

 irogen gas is unstable. 



This, it must be confessed, is but a crude mode of explain- 



