306 DISCUSSIONS IN COSMOLOGY. 



pound of the mass, and a cubic foot of the sun at his 

 present density of 1*43 weighing 89 lbs., each cubic 

 foot must have possessed 8,900,000,000,000 foot- 

 pounds. But when the mass was expanded to occupy 

 274,000,000,000 times more space, which it would do 

 when it extended to the orbit of Neptune, the heat 

 possessed by each cubic foot would then amount to 

 only 32 foot-pounds. 



In point of fact, however, it would not even amount 

 to that ; for a quantity equal to upwards of 20 million 

 years' heat would necessarily be consumed in work 

 against gravity in the expansion of the mass ; all of 

 which would, of course, be given back in the form of 

 heat as the mass contracted. During the nebulous 

 condition it would not exist as heat, so that only 19 

 foot-pounds out of the 32 foot-pounds generated by 

 concussion would then exist as heat. The density of 

 the nebula would be only T e <? Are o that of hydrogen at 

 ordinary temperature and pressure. The 19 foot- 

 pounds of heat in each cubic foot would nevertheless 

 be sufficient to maintain an excessive temperature; for 

 there would be in each cubic foot only t^oWo of a grain 

 of matter. But although the temperature would be 

 excessive, the quantity both of light and heat in each 

 cubic foot would of necessity be small. The heat being 

 only tt of a thermal unit, the light emitted would 

 certainly be exceedingly feeble, resembling very much 

 the electric light in a vacuum-tube. 



Heat and Light of Nebulas cannot result from Con- 

 densation. — The fact that nebulse are not only self- 

 luminous but indicate the existence of hydrogen and 

 nitrogen in an incandescent condition proves that they 

 must possess a considerable temperature. And it is 

 scarcely conceivable that the temperature could have 

 been derived from the condensation of their masses. 



