40 A CENTURY'S PROGRESS IN ASTRONOMY. 



Milky Way, stating that his telescopes could 

 not fathom it. This was the abandonment of his 

 second assumption namely, that his telescope 

 was sufficiently powerful to penetrate to the 

 limits of the Universe. Yet he still thought 

 that some of the star-clusters might be external 

 galaxies, although he could not even dogmati- 

 cally assert our Universe to be limited. In an 

 error of translation, Struve left the impression 

 that Herschel believed our Universe to be un- 

 fathomable or infinite, and was obliged to devise 

 a most artificial theory of the extinction of light 

 to account for the fact that the sky did not 

 shine with the brilliance of the Sun, which it 

 would do were the stars infinite in number. Of 

 course, Herschel did not actually believe the 

 Universe to be infinite, and, had he lived, he 

 would probably have shown that all the star- 

 clusters which we see are included within the 

 bounds of our finite Galaxy. 



In 1814 Herschel was "still engaged in a 

 series of observations for ascertaining a scale 

 whereby the extent of the Universe, as far as it 

 is possible for us to penetrate into space, may be 

 fathomed." In 1817 he described another method 

 of star-gauging, which Arago and other writers 

 have confused with that which he devised in 

 1785. The two methods, however, were quite 



