192 FROM NEBULA TO NEBULA 



is falling in temperature in the process of shrinking are 

 right. The sun may, in fact, not be shrinking at all, but 

 simply holding his own ! For let us hark back to the time 

 when the luminary may be supposed to have possessed 

 double his present diameter, and to have had a tempera- 

 ture, say, twice as high as at present. Then, according 

 to Stefan's law, his radiation, area for area, must have 

 been increased in the ratio of the fourth poiver, or sixteen 

 times, and his surface area being concurrently multiplied 

 by four, his total radiation must, according to figures, 

 have been 64 times as copious then as it is to-day ob- 

 viously contrary to the biological facts. Indeed, the sun 

 dare not even be postulated as at that time possessing the 

 same temperature as now, inasmuch as he would then 

 have been radiating four times as much heat, on account 

 of his greater area ;which would have meant the total 

 destruction of all terrestrial life then extant. 



That the Helmholtzian hypothesis leaves much to be 

 desired is well recognized now, though scientists were 

 loth to admit it prior to the discovery of radium in 1898, 

 when a new hope dawned. Since then, zealous efforts 

 have been made to discover traces of radium in the solar 

 spectrum, but so far without success. Professor S. A. 

 Mitchell, of Yerkes Observatory, writing in 1913 (Pop. 

 Astr., No. 206), reports thus : 



From theoretical considerations we are positively convinced 

 that there must be radium in the sun. But to prove this is an- 

 other problem. With the spectra we already have we can prove 

 nothing more than accidental coincidences. One of the problems 

 for the solar eclipse of August, 1914, will be to obtain the spec- 

 trum of the chromosphere on a large scale with good definition 

 so that we may prove what we think we know, that radium is in 

 the sun. [The eclipse mentioned developed nothing new.] 



If I interpret this quotation correctly, here is an in- 

 timation that if ever astrophysicists succeed in finding 

 even so much as an indubitable trace of radium existing 

 in the sun, the whole vexing problem of the source of the 

 solar heat will be labeled ' ' solved ? ' and put away on the 

 shelf for keeps. But the radium hypothesis can never 

 solve this problem finally, no matter if the sun be proved 



