CH. XXX. THE PLANET URANUS. 273 



thought at first that he had discovered a comet, but it was 

 not long before his wandering star was proved to be a new 

 planet, moving round the sun outside Saturn. This planet 

 is about half the size of Saturn, and takes more than eighty- 

 four years to go once round the sun. It was first called the 

 * Georgian star,' after George III. ; then it was called * Her- 

 schel,' after its discoverer; and lastly it received the name 

 Ut'anus, 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 himself 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 bright- 

 ness. Thus he classed the most brilliant as stars of the 

 first magnitude, those a little less brilliant as of the second 

 magnitude, and so on. 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 these stars ap- 

 peared close together 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 these stars, 

 instead of merely passing to and fro in a straight line across 

 each other, as they would appear to do in consequence of 



