PART VII. 

 THE NEW KNOWLEDGE AND OLD PROBLEMS. 



CHAPTER I. 

 COSMIC AL PROBLEMS AND RADIO-ACTIVITY. 



THE SUN'S HEAT. 



How does the sun maintain its heat? This has always 

 been a problem of intense interest to the human mind. It 

 was at first supposed, naively, that the sun's heat was 

 maintained by ordinary chemical combustion; that the sun 

 was a burning fire, and that when the coal, or what not, of 

 which the sun was composed, was consumed, there would be 

 an end of light and heat and life. This belief was shown to 

 be untenable, among others by Professor Tait who said: 

 "Take (in mass equal to the sun's mass) the most energetic 

 chemicab known to us and the proper proportion for giv- 

 ing the gr3atest amount of heat by actual chemical combi- 

 nation and, so far as we yet know their properties, we can- 

 not see the means of supplying the sun's present waste 

 for even 5,000 years. ... It is quite obvious that the 

 heat of the sun cannot possibly be supplied by any chem- 

 ical process of which we have the slightest conception. 

 . . . This question is quite unanswerable, unless there be 

 chemical agencies at work in the sun of a far more powerful 

 order than anything we meet with on the earth's surface." 



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