208 THE BORDERLAND OF SCIENCE. 



that the major planets were once in the condition of suns 

 (even if they are not at the present time the scene of 

 processes resembling solar action) ; and (3) if a large 

 sun can expel matter from his globe with the enormous 

 velocity necessary to carry such matter for ever away 

 from him, it is more than conceivable that smaller suns 

 should be competent to expel matter from their sub- 

 stance with the much smaller velocity necessary to free 

 such matter from the attraction of the parent planet. 

 It might also be added, that since we explain the 

 downfall of heavy masses as due to solar eruptive 

 energies, it appears reasonable to infer that the ' lighter 

 metal' of the shooting-stars is due to the eruptive 

 energies of minor suns. And it would appear to 

 confirm this opinion that so far as observations have 

 hitherto extended, all the meteoric streams which 

 really belong to the solar system (and thus come under 

 the above reasoning) produce displays of shooting-stars 

 only, not casting down upon the earth any aerolitic 

 masses, while all the comets which are of comparatively 

 short period are in like manner of secondary importance 

 as respects their dimensions. 



Nevertheless, it is obviously desirable that a theory 

 so surprising should be supported by independent 

 evidence. It is, indeed, always a strong point in favour 

 of a theory that it is one to which we appear to be 

 driven by the failure of all others which had suggested 

 themselves. But it is characteristic of a true theory 

 that it not only meets the particular difficulties which 

 have driven the reasoner towards it, but supplies an 



