34 d Short History of Astronomy [CH. xil. 



body ; so that condensation could be regarded as a sign 

 of " age." And he goes on : 



" This method of viewing the heavens seems to throw them 

 into a new kind of light. They are now seen to resemble a luxu- 

 riant garden, which contains tbe greatest variety of productions, in 

 different flourishing beds ; and one advantage we may at least 

 reap from it is, that we can, as it were, extend the range of 

 our experience to an immense duration. For, to continue the 

 simile I have borrowed from the vegetable kingdom, is it not 

 almost the same thing, whether we live successively to witness 

 the germination, blooming, foliage, fecundity, fading, withering 

 and corruption of a plant, or whether a vast number of 

 specimens, selected from every stage through which the plant 

 passes in the course of its existence, be brought at once to 

 our view ? " 



His change of opinion in 1791 as to the nature of nebulae 

 led to a corresponding modification of his views of this 

 process of condensation. Of the star already referred to 

 ( 260) he remarked that its nebulous envelope " was more 

 fit to produce a star by its condensation than to depend upon 

 the star for its existence." In 1811 and 1814 he published 

 a complete theory of a possible process whereby the shining 

 fluid constituting a diffused nebula might gradually con- 

 dense the denser portions of it being centres of attraction 

 first into a denser nebula or compressed star cluster, then 

 into one or more nebulous stars, lastly into a single star 

 or group of stars. Every supposed stage in this process 

 was abundantly illustrated from the records of actual nebulae 

 and clusters which he had observed. 



In the latter paper he also for the first time recognised 

 that the clusters in and near the Milky Way really belonged 

 to it, and were not independent systems that happened to 

 lie in the same direction as seen by us. 



262. On another allied point Herschel also changed his 

 mind towards the end of his life. When he first used his 

 great 20-foot telescope to explore the Milky W T ay, he thought 

 that he had succeeded in completely resolving its faint 

 cloudy light into component stars, and had thus penetrated 

 to the end of the Milky Way ; but afterwards he was con- 

 vinced that this was not the case, but that there remained 

 cloudy portions which whether on account of their remote- 



