RELATIVE ANTIQUITY OF NEBULA 147 



that this ocean of ether is in any degree impervious 

 to light. His friend Dr. Olbers, of Bremen, suggested 

 that it might be. Precisely as the glass or the horn, 

 through which rays of light pass, keeps part of them 

 back or absorbs them, the infinite ocean of ether may 

 have a similar effect, though in a vastly less degree. 

 This apprehension remains a mere speculation to this 

 day. Sometimes these islands of stars were broken 

 into clusters of stars showing magnificent colours, 

 and forming the most splendid objects that can be 

 seen in the heavens. They seemed to concentrate 

 round a centre. The Milky Way is one of these islands, 

 of which the population consists in suns and worlds. 

 Others, separated from it and from each other, and 

 even apparently changing their shape from age to age, 

 are " generally seen upon a very clear and pure ground 

 without any star near them that might be supposed to 

 belong to them." With all this sublimity of exposition 

 and explanation, Herschel at the same time asks for con- 

 sideration from critics and readers, "for, this subject 

 being so new, I look upon what is here given partly as 

 only an example to illustrate the spirit of the method." 

 The idea Herschel formed and then figured of the 

 shape of the Milky Way may be best understood 

 by comparing it to the palm of the hand with only 

 two fingers the middle and the forefinger and these 

 stretched fully out. Our sun he supposed to be near 

 the roots of the fingers, looking out into open space 

 through the interval between them. He had the idea 

 also that our star-island " has fewer marks of antiquity 

 upon it than the rest." He believed that its stars 

 " are now drawing towards various secondary centres, 

 and will in time separate into different clusters so as 



