CH. xxxi. THE PLANET URANUS. 283 



it received the name Uranus, which it still retains. It was 

 through this discovery that Herschel became known, and 

 George III. gave him a pension of 300 guineas a year, and 

 a house near Windsor, in order that he might devote him- 

 self entirely to astronomy. 



Star-gauging and Discovery of Binary Stars, 1781- 

 1802. One of the first tasks which Herschel undertook was 

 to divide the stars into groups, according to their brightness, 

 and to gauge the heavens by estimating the number of stars 

 of each order of brightness, thus endeavouring to estimate 

 the profundity of space. While he was thus gauging^ or 

 measuring the distance of the stars by the intensity of their 

 light, his attention was arrested by some which appear 

 single when seen through a small telescope, but which prove 

 to be two stars when they are greatly magnified. A few of 

 these double stars were known already when Herschel began 

 to observe them, but he soon detected no less than 500 

 scattered about in different parts of the sky. 



Now it had always been believed that the reason why 

 these stars appeared close together was because one was 

 almost directly behind the other a long way off, just as two 

 posts standing one at some distance behind the other will 

 appear to touch if they are nearly on a line with your eye. 

 But this explanation did not satisfy Herschel, for he observed 

 that many of the double stars, instead of merely passing to and 

 fro in a straight line across each other, as they would appear 

 to do in consequence of the movement of our earth in its 

 orbit, had another peculiar curved motion, as if they were 

 both moving round some point half-way between them. 

 This movement was so slow that it was twenty-five years 

 before he could be sure about it ; but at the end of this 

 time he was able to tell the Royal Society that these double 

 or binary stars, as they are called, are not one behind the 



