224 FROM NEBULA TO NEBULA 



second of arc, so that, so far as telescopic observation is con- 

 cerned, the contraction theory is tenable, for a change of i/io 

 second in the solar diameter is unrecognizable. From calcula- 

 tions of Newcomb the sun will require to have shrunk to one- 

 half its present size if it maintains its present rate or radiation for 

 about 7,000,000 years longer. 



On the same subject Doctor Young (Genl. Astr., Art. 

 359) says: 



As to the past of the Solar history on this hypothesis (Helm- 

 holtz's), we can be a little more definite. It is only necessary to 

 know the present amount of radiation, and the mass of the sun, 

 to compute how long the solar fire can have been maintained at 

 its present intensity by the processes of condensation. No con- 

 clusion of geometry is more certain than this, that the contrac- 

 tion of the sun to its present size, from a diameter even many 

 times greater than Neptune's orbit, would have furnished about 

 18,000,000 times as much heat as the sun now supplies in a year, 

 and therefore that the sun cannot have been emitting heat at the 

 present rate for more than 18,000,000 years, if its heat has really 

 been generated in this manner. 



But this conclusion rests upon the assumption that the sun 

 has derived its heat solely in this way, and the recent discoveries 

 with respect to radium and radio-activity strongly suggest other 

 causes which may have added large contributions, and may still 

 be operative in maintaining the solar radiation. 



Apropos of the same subject we may add this from 

 Doctor Newcomb (Art. Sun, Americana) : 



If the sun were merely losing energy like an ordinary hot 

 body cooling off, a very simple calculation will show that it would 

 be so cooled off in the course of 3,000 or 4,000 years as no longer 

 to radiate much heat. It is clear that such has not been the case. 

 Yet the most careful study shows no possibility that it can be re- 

 ceiving energy from any outside source. Moreover, the geolo- 

 gists assure us that the stratification of the rocks, as well as many 

 other phenomena associated with them, proves that the sun has 

 been radiating heat to the earth at not much less than its present 

 rate for hundreds of millions of years. 



How fertile in expedients, these astronomers, and 

 how well they love to eat their cake and have it too! 

 Consider, if you please, these facts : Away back in 1853, 

 when Helmholtz put forth this explanation, the Laplacian 

 hypothesis was in its heyday, and not a voice in the land 



