SOME UNSOLVED SCIENTIFIC PROBLEMS 



planets. So another source of the sun's energy had to 

 be sought. It was found forthwith by that other great 

 German, Helmholtz, who pointed out that the falling 

 matter through which heat may be generated might 

 just as well be within the substance of the sun as with- 

 out mother words, that contraction of the sun's heated 

 body is quite sufficient to account for a long-sustained 

 heat-supply which the mere burning of any known 

 substance could not approach. Moreover the amount 

 of matter thus falling towards the sun's centre being 

 enormous namely, the total substance of the sun a 

 relatively small amount of contraction would be theo- 

 retically sufficient to keep the sun's furnace at par, so 

 to speak. 



At first sight this explanation seemed a little puzzling 

 to many laymen and some experts, for it seemed to im- 

 ply, as Lord Kelvin pointed out, that the sun contracts 

 because it is getting cooler, and gains heat because it 

 contracts. But this feat is not really as paradoxical as 

 it seems, for it is not implied that there is any real gain 

 of heat in the sun's mass as a whole, but quite the re- 

 verse. All that is sought is an explanation of a main- 

 tenance of heat-giving capacity relatively unchanged 

 for a long, but not an interminable, period. Indeed, ex- 

 actly here comes in the novel and startling feature of 

 Helmholtz's calculation. According to Mayer's me- 

 teoric hypothesis, there were no data at hand for any 

 estimate whatever as to the sun's permanency, since 

 no one could surmise what might be the limits of the 

 meteoric supply. But Helmholtz's estimate implied 

 an incandescent body cooling keeping up a some- 

 what equable temperature through contraction for a 



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