The Romance of the Heavens 27 



outer one-mile thickness would have a straight drop of one mile 

 towards the centre. And that is not all, because obviously the 

 layers below this outer mile would also drop inwards, each to a 

 less degree than the one above it. What a tremendous movement 

 of matter, however slowly it might take place ! And what a tre- 

 mendous energy would be involved ! Astronomers calculate that 

 the above shrinkage of one mile all round would require fifty 

 years for its completion, assuming, reasonably, that there is close 

 and continuous relationship between loss of heat by radiation and 

 shrinkage. Even if this were true we need not feel over-anxious 

 on this theory; before the sun became too cold to support life 

 many millions of years would be required. 



It was suggested at one time that falls of meteoric matter 

 into the sun would account for the sun's heat. This position is 

 hardly tenable now. The mere bulk of the meteoric matter re- 

 quired by the hypothesis, apart from other reasons, is against it. 

 There is undoubtedly an enormous amount of meteoric matter 

 moving about within the bounds of the solar system, but most of 

 it seems to be following definite routes round the sun like the 

 planets. The stray erratic quantities destined to meet their doom 

 by collision with the sun can hardly be sufficient to account for the 

 sun's heat. 



Recent study of radio-active bodies has suggested another 

 factor that may be working powerfully along with the force of 

 gravitation to maintain the sun's store of heat. In radio-active 

 bodies certain atoms seem to be undergoing disintegration. These 

 atoms appear to be splitting up into very minute and primitive 

 constituents. But since matter may be split up into such con- 

 stituents, may it not be built up from them? 



The question is whether these "radio-active" elements are 

 undergoing disintegration, or formation, in the sun. If they are 

 undergoing disintegration and the sun itself is undoubtedly 

 radio-active then we have another source of heat for the sun 

 that will last indefinitely. 



