THE BIRTH OP THE Sun AND PLANETS 23 



greater than the heat given in any ordinary chemical 

 combination of atoms. It would Le Bon calculates 

 take 340,000 barrels of powder to send off a bullet at the 

 rate at which the electrons fly out of the atom of radium. 

 Here is a source of energy so appalling and unexpected 

 that Lord Kelvin long refused to credit the facts. We 

 have only to suppose that there are large quantities of 

 radium in the sun, and the whole problem of the continu- 

 ance of its heat is changed. Many astronomers (like 

 Meyer) maintain that there are millions of tons of radium 

 in it that the terrific electric storms it sends to us, 

 especially from the margins of its " spots," are radio- 

 emanations. However we may esteem the evidence, the 

 possibility remains, and the age of the sun may be 

 indefinitely greater than was supposed.* 



It is now therefore quite useless to conjecture, on the 

 old lines, what the age of our system may be. I will, in 

 conclusion, merely quote the words of one most com- 

 petent to express an opinion on the subject, Sir G. H. 

 Darwin. The birth of the moon from the earth is, we 

 saw, an episode in the life of our solar system, that dates 

 some long time after the first movement of the nebula 

 (or meteorites). Now, Sir G. H. Darwin is responsible 

 for one of the most commanding theories on the origin 

 of the moon, and in his presidential address to the 

 British Association in 1905 he says in regard to the 

 remoteness of that event : 



"If at every moment since the birth of the moon 

 tidal friction had always been at work in such a way 

 as to produce the greatest possible effect, then we 



* It is sometimes objected that, as the life of an atom of 

 radium is computed to be only about 2,450 years, there cannot 

 have been radium in earlier times. But it may be forming in 

 the sun as constantly as it is breaking up. It is said though 

 some deny this to be evolving out of uranium under our eyes. 



