a part ; while the fainter stars in the 

 depths of space may be grouped in other 

 stellar systems. Thus he thought the 

 nebulae were separated universes of stars, 

 so far away as to defy resolution into 

 their components. Modern astronomical 

 theories are now moving, of course far 

 more definitely, along similar lines, forti- 

 fied by the immense masses of facts 

 relating to distances, motions and con- 

 stitutions of the stars and nebulae, which 

 are provided by the photographic plate 

 and the spectroscope in conjunction with 

 large telescopes. 



" In Michell's day the available data 

 were utterly inadequate to guide to safe 

 statistical conclusions on matters of such 

 delicate inference. But the mathematical 

 modes of reasoning in his Memoir of 1767 

 are still of much interest in the light of 

 modern knowledge, especially as they are 

 illustrated by a discussion of the group of 

 the Pleiades, as it is presented to the naked 

 eye and also in telescopes of various aper- 

 102 



