310 DISCUSSIONS IN COSMOLOGY. 



should have what Professor Tait has suggested, a 

 nebula consisting of "clouds of stones." But such 

 nebulae must be of rare occurrence. 



Objections considered. — On a former occasion I con- 

 sidered one or two anticipated objections to the theory 

 that stellar light and heat were derived from motion 

 in space. But as these objections have since been 

 repeatedly urged by physicists both in this country 

 and in America, I shall again briefly refer to them. 



Objection 1st. "The existence of such non-luminous 

 bodies as the theory assumes is purely conjectural, as 

 no such bodies have ever been observed." In reply, it 

 is just as legitimate an inference that there are bodies 

 in stellar space not luminous as that there are luminous 

 bodies in space not visible. We have just as good 

 evidence for believing in the existence of the one as 

 we have in the existence of the other. Bodies in 

 stellar space can only be known through the eye to 

 exist. If they are not luminous, they of course cannot 

 be seen. But we are not warranted on that account 

 to suppose that they do not exist, any more than we 

 have to suppose that stars do not exist which are 

 beyond the reach of our vision. We have, however, 

 positive evidence that there are bodies in space non- 

 luminous, as the meteorites and planets for example. 

 The stars are beyond doubt suns like our own; and 

 we cannot avoid the inference that, like our sun, they 

 are surrounded by planets. If so, then we have to 

 admit that there are far more bodies in stellar space 

 non-luminous than luminous. But this is not all : the 

 stars no more than our sun can have been dissipating 

 their light and heat during all past ages ; their light 

 and heat must have had a beginning ; and before that 

 they could not be luminous. Neither can they con- 

 tinue to give out light and heat eternally ; conse- 



