THE FUEL OF THE SUX. 79 



There will, however, be somewhere an elevation at which 

 the heat evolved by the joint compression of the elementary 

 and combined gases will be just sufficient to dissociate the 

 latter, and here will be the meeting surface of the combined 

 and the uncombined constituents of water. There will be a 

 sphere containing uncombined oxygen and hydrogen sur- 

 rounded by an atmospheric envelope containing large quanti- 

 ties of aqueous vapor, and the temperature at this limiting 

 surface will be equal to that of the oxyhydrogen flame under a 

 corresponding pressure. 



What will occur under these conditions ? Will the " detonat- 

 ing gases" bchaVe as in the laboratory ? Obviously not, as a 

 glance at the third of the above parallel propositions will show. 

 The dissociated gases cannot combine without giving off their 

 4532 of latent heat as actual temperature. This can only be 

 effected by communication with matter which is cooler than 

 itself. 



If a bubble of steam is surrounded by water maintained at 

 the boiling temperature, it will not condense at all, because 

 any effort of condensation would be accompanied with an 

 evolution of heat exactly sufficient to evaporate its own result. 

 If, however, the surrounding water is slowly radiating, or 

 otherwise losing its heat, the inclosed bubble of steam will 

 condense proportionately, by giving off to its envelope an 

 amount of its latent heat just sufficient to maintain the water 

 at the boiling-point. 



For further illustration, let us conceive the case of a certain 

 quantity of tliG elements of water heated exactly to the tem- 

 perature of dissociation, and confined in a vessel the sides of 

 which are maintained externally at precisely the same tempera- 

 ture as the gases within, so that no heat can be added or taken 

 away from them. No sensible amount of combination can. 

 take place, as the first infinitesimal effort of combustion, or 

 combination, would set free just the amount of heat require' 

 to decompose its own result. Let us now suppose a modific. 



doing far greater dissociation work than that which separates the 

 hydrogen of the prominences revealed by the spectroscope. In. 

 putting forth this "working hypothesis" he seems to have lost sight 

 of the fact clearly proved by Deville's experiments, that the tem- 

 perature of dissociation rises with the pressure to which the com- 

 pound is subjected, and thus that within the bowels of the sun the 

 metals will be far less dissociable than they are on the surface of our 

 earth. 



