8 FROM NEBULA TO NEBULA 



of the mechanical equivalent of heat had its birth, and it 

 was then immediately contended that the Nebula must 

 have been cold to start with, but that the kinetic energy 

 developed by the falling together of its component mat- 

 ter into the large bodies of the sun and planets initially 

 heated them in a degree proportional to their respective 

 masses. Mathematicians, however, soon showed that, so 

 far, at least, as the sun was concerned, the new hypothe- 

 sis was absurdly below requirements ; and this finding it 

 was that evoked the suggestion from Helmholtz that the 

 sun is still a contracting body, that is to say, one in which 

 the energy due to " position " is still in process of conver- 

 sion into kinetic energy. Although this theory was 

 tenaciously adhered to for decades, in spite of its geologi- 

 cal contradictions, it finally succumbed to the joint attack 

 of the mathematician's pencil and the new champion, 

 Eadium. But alas, and alas !, according to Doctor S. A. 

 Mitchell (Pop. Astr., June, 1913) : 



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 but coincidences. 



In a nutshell, then, the source of the sun 's heat is still 

 a wide-open question. 



THE GENESIS or THE SOLAR SYSTEM 



For nearly three quarters of a century, and until a 

 decade or two ago, the Nebular Hypothesis of Laplace 

 was generally esteemed as the true exposition of the 

 modus operandi pursued by Nature in the evolution of the 

 solar system. Now it is no longer so regarded by the 

 great majority of astronomers, and, more particularly, by 

 those who have made this subject a special study. Al- 

 though it is quite true that numerous other hypotheses 

 have arisen to compete for its vacated place, the fall of 

 the Hypothesis has not been owing so much to their suc- 

 cessful rivalry as to the belated recognition of its own 

 glaring defects. As a matter of fact, never since Newton 



