ON THE OKIGIN OF THE PLANETAKY SYSTEM. 181 



which was propounded by Mayer, and has been favour- 

 ably adopted by several other physicists, is open, ac- 

 cording to Sir W. Thomson's investigations, to ob- 

 jection ; for, assuming it to hold, the mass of the 

 sun should increase so rapidly that the consequences 

 would have shown themselves in the accelerated 

 motion of the planets. The entire loss of heat from 

 the sun cannot at all events be produced in this way ; 

 at the most a portion, which, however, may not be 

 inconsiderable. 



If, now, there is no present manifestation of force 

 sufficient to cover the expenditure of the sun's heat, 

 the sun must originally have had a store of heat which 

 it gradually gives out. But whence this store ? We 

 know that the cosmical forces ^lone could have pro- 

 duced it. And here the hypothesis, previously dis- 

 cussed as to the origin of the sun, comes to our aid. If 

 the mass of the sun had been once diffused in cosmical 

 space, and had then been condensed that is, had fallen 

 together under the influence of celestial gravity if 

 then the resultant motion had been destroyed by 

 friction and impact, with the production of heat, the 

 new world produced by such condensation must have 

 acquired a store of heat not only of considerable, but 

 even of colossal, magnitude. 



Calculation shows that, assuming the thermal capa- 

 city of the sun to be the same as that of water, the 



