24 IN STARRY REALMS. 



would have become cold and dark ages ago if it had no 

 further heat than this supposition implies. We then 

 investigated whether there could be any sufficient supply 

 of something analogous to fire, so that the sun's heat 

 could be maintained by combustion. This, again, will 

 not stand the necessary test : it is wholly impossible that 

 material of the required character should be forthcoming 

 in sufficient abundance. Finally, we have examined the 

 notion that the sun's heat may be produced by the fric- 

 tion of meteors which dash into his atmosphere. This 

 source of supply may be a small rate-in-aid of the sun's 

 current expenditure, but cannot explain how the bulk of 

 that expenditure has to be provided for. 



We have now to set forth the true explanation, which 

 has been universally adopted whenever the evidence in its 

 favour has been duly considered. The question is by no 

 means an easy one, but I shall strive to make it as clear 

 as circumstances will permit. A multitude of observations 

 point irresistibly to the conclusion that the sun is not a 

 solid body. In this respect we may contrast the sun with 

 the moon. Our satellite is eminently a solid as opposed 

 to a gaseous object ; every feature on the moon is perma- 

 nent and definitely marked, and can be observed from 

 year to year in the same place and with the same sur- 

 roundings. But there seems to be no permanent object 

 whatever visible on the sun. In fact, it would be a great 

 convenience to astronomers if there were some solid moun- 

 tain peak which would mark one definite locality on the 

 sun's globe. We are sadly in want of some such definite 

 feature to serve as an origin from which the longitude of 

 spots or other objects on the sun's globe could generally 



