HEAT. 51 



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 hypothesis which I can 

 frame is by assuming that the constituent molecules of water 

 are, below a certain temperature, in a state of stable equili- 

 brium ; that the molecules of mixed or oxyhydrogen gas are, 

 above a certain temperature, also in a state of stable equili- 

 brium, but of an opposite character ; while below this latter 

 temperature the molecules of mixed gas are in a state of un- 

 stable 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 between 

 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 re- 

 spectively within the range of attractive force ; or, supposing 

 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 retain 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 attractive force 

 of all the molecules may be overcome, and decomposition 

 ensue. Thus, water or steam below a certain temperature, 

 and mixed gas above a certain temperature, may be supposed 

 to be in the state of stable equilibrium, whilst between these 

 limiting temperatures, the equilibrium of oxyhydrogen gas is 

 unstable. 



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

 ing the phenomena, and requires the assumption, that chemical 

 attraction or affinity, as it is awkwardly termed, has similar 

 attributes to physical attraction. Chemical affinity holds 

 good between the particles of matter when it is in a gaseous 

 state, and though gases do not give evidence of the physical 



E 2 



