ON THE AGE OF THE SUN'S HEAT. 367 



at mutual distances all large in comparison with 

 their diameters, and forming a globe of uniform 

 density equal in mass and diameter to the sun, 

 would generate an amount of heat which, ac- 

 curately calculated according to Joule's principles 

 and experimental results, is found to be just 

 20,000,000 times Pouillet's estimate of the annual 

 amount of solar radiation. The sun's density 

 must, in all probability, increase very much towards 

 his centre, and therefore a considerably greater 

 amount of heat than that must be supposed to 

 have been generated if his whole mass was 

 formed by the coalition of comparatively small 

 bodies. On the other hand, we do not know 

 how much heat may have been dissipated by re- 

 sistance and minor impacts before the final 

 conglomeration ; but there is reason to believe 

 that even the most rapid conglomeration that we 

 can conceive to have probably taken place, could 

 only leave the finished globe with about half the 

 entire heat due to the amount of potential energy 

 of mutual gravitation exhausted. We may, there- 

 fore, accept, as a lowest estimate for the sun's 



