304 THE ADDRESSES, LECTURES, ETC., OF 



duced, owing to its mighty proportions, would flow outward into 

 space, to a practically unlimited distance. 



The next question for consideration is : What would become of 

 these products of combustion when thus returned into space ? 

 Apparently they would gradually change the condition of stellar 

 material, rendering it more and more neutral ; but I venture to 

 suggest the possibility, nay, the probability, that solar radiation 

 will, under these conditions, step in to bring back the combined 

 materials to a state of separation by dissociation carried into effect 

 at the expense of that solar energy which is now supposed to be 

 irrevocably lost or dissipated into space as the phrase goes. 



According to the law of dissociation as developed by Bunsen 

 and Sainte-Claire Deville, the point of decomposition of different 

 compounds depends upon the temperature on the one hand, and 

 upon the pressure on the other. According to Sainte-Claire 

 Deville, the dissociation tension of aqueous vapour at atmospheric 

 pressure and at 2800 C. is 0'5, that is to say one half of the 

 vapour would exist as such, the remaining half being found as a 

 mechanical mixture of hydrogen and oxygen ; but with the 

 pressure, the temperature of dissociation rises and falls, as the 

 temperature of saturated steam rises and falls with its pressure. 

 It is therefore conceivable that the solar photosphere may be 

 raised by combustion to a temperature exceeding 2800 C., whereas 

 dissociation may be effected in space at a lower temperature. 

 This temperature of. 2800 would be quite sufficient to account for 

 the character and amount of solar radiation, if it is only borne in 

 mind that the luminous atmosphere may be a thousand miles in 

 depth, and that the flame of hydrogen and hydrocarbons, in the 

 uppermost layers of this zone, is transparent to the radiant energy 

 produced in the layers below, thus making the total radiation 

 rather the sum of matter in combustion than the effect of a very 

 intensely heated surface. 



Sainte-Claire Deville's investigations had reference only to 

 heats measured by means of pyrometers, but do not extend to 

 the effects of radiant heat. Dr. Tyndall has shown by his 

 important researches that vapour of water and other gaseous 

 compounds intercept radiant heat in a most remarkable degree, 

 and there is other evidence to show that radiant energy from a 

 source of high intensity possesses a dissociating power far sur- 



