14 SCIENCE IN SHORT CHAPTERS. 



With the general laws of the dissociation of water thus 

 before us,* we may follow out the necessary action of the 

 above-stated pressure and consequent evolution of heat in 

 the lower regions of the solar atmosphere upon the large 

 proportion of aqueous vapor which I have shown that it 

 should contain. 



It is evident that the first result will be separation of 

 this water into its elements, accompanied with a loss of 

 temperature corresponding to the latent heat of dissocia- 

 tion. We may assume that in the lower regions of the solar 

 atmosphere the free heat evolved by mechanical compression 

 will be more than sufficient to dissociate the whole of the 

 aqueous vapor, and thus the dissociated gases will be left 

 at a higher temperature than was necessary to effect their 

 dissociation. Their condition will thus be analogous to that 

 of superheated steam: they will have to give off some heat 

 before they can begin to combine.* 



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 combined oxygen and hydrogen sur- 

 rounded by an atmospheric envelope containing large quan- 

 tities 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 " de- 



* Since the publication of "The Fuel of the Sun," Mr. Norman 

 Lockyer has adopted this view of solar dissociation, and has gone so 

 far ns* to suppose that it splits metals and other substances regarded by 

 modern chemists as simple elements into more elementary and simple 

 constituents. He assumes that the temperature of the solar atmos- 

 phere, growing higher at increasing depths, becomes somewhere cap- 

 able of "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 tempera- 

 ture of dissociation rises with the pressure to which the compound is 

 subjected, and thus that within the bowels of the sun the metals will 

 be far less dissociable than they art on the surface of our earth. 



