102 SCIEN.OB IN SHORT CHAPTERS. 



necessary, in order to do justice to Dr. Siemens, to always keep 

 in mind the assumed condition of a universal and continuous 

 atmospheric medium, and not to reason, as some have done 

 already, upon the basis of a limited solar atmosphere with a 

 definite boundary, from beyond which particles of atmospheric 

 matter are to be flung away into vacuous space, without the 

 intervention of all-pervading fluid pressure. 



It is evident that if such fan action can bring back all the 

 material that has received the solar radiations, and which 

 holds them either as temperature or otherwise, the restoration 

 and perpetuation of solar energy will be complete, for even the 

 heat received by our earth and its brother and sister planets 

 would still remain in the family, as they would radiate it into 

 the interplanetary atmospheric matter supposed to be reclaimed 

 by the sun. 



But, as Mr. Proctor has clearly shown, the rays of the sun 

 cannot do all the work thus required for his own restoration 

 without becoming extinguished as regards the outside universe ; 

 and if the other suns i.e. the stars do the same they could 

 not be visible to us. 



Thus Dr. Siemens's theory removes our sun from his place 

 among the stars, and renders the great problem of stellar radia- 

 tion more inscrutable than ever by thus putting the evidence of 

 our great luminary altogether out of court. 



My theory, on the contrary, demands only a gradual absorp- 

 tion of solar and stellar rays, such as actual observation of their 

 varying splendor indicates. 



If space were absolutely transparent, and its infinite depths 

 peopled throughout, the firmament would present to our view 

 one continuous blazing dome, as all the spaces between the. 

 nearer stars would be filled by the infinity of radiations from 

 the more distant. 



CHAPTER XIV. 



THE ORIGIN OF LUNAR VOLCANOES. 



MANY theoretical efforts, some of considerable violence, have 

 been made to reconcile the supposed physical contradiction pre- 

 sented by the great magnitude and area of former volcanic 

 activity of the Moon, and the present absence of water on its 



