THE HERSCHELS AND THE STAR-DEPTHS. I/ 



Sir John Herschel has also exhibited the relations of 

 this theory of external Milky Ways, in passages of a 

 striking nature. In 'one respect, indeed, he has passed 

 even beyond the limits ranged over by his father's 

 daring ideas, insomuch that while Sir W. Herschel 

 spoke only of systems of Milky Ways, his son has urged 

 the idea of systems of such systems, and has even 

 suggested the possibility that some of the celestial 

 cloudlets may belong to this higher order. ' To us,' he 

 says, fi the material universe must be regarded as practi- 

 cally infinite, seeing that we can perceive no reason 

 which can place any bounds to the further extension of 

 that principle of systematic subordination which has 



already been traced to a certain extent It 



by no means follows that all those objects which stand 

 classed under the general designation of " nebulae " or 

 " clusters of stars," and of which the number already 

 known amounts to upwards of five thousand, are objects 

 of the same order. Among those dim and mysterious 

 existences, which only a practised eye, aided by a 

 powerful telescope, can pronounce to be something 

 different from minute stars, may, for anything we can 

 prove to the contrary, be included systems of a higher 

 order than that which comprehends all our nebulse 

 (properly such), reduced by immensity of distance to 

 the very last limit of visibility.' 



But we must distinguish between that which is 

 possible or even probable, and that which the astrono- 

 mer has been able to demonstrate. If we examine the 

 progress of Sir W. Herschel's researches into the 



c 



