J02 



NINETEENTH CENTURY. PT. in. 



time it was expected, and was seen each night afterwards as 

 usual till January 12. On that night, however, when 

 Lieutenant Maury looked at it from the observatory at 

 Washington, in the United States, he saw, not one comet, 

 bat two distinct and separate comets moving along together. 

 This seemed so strange that it would scarcely have been 

 believed if several astronomers had not watched the comet 

 for more than a month, and satisfied themselves that it had 

 really split up into two parts, each part being a perfect 

 comet, with a bright head and a glowing tail ! These two 

 comets returned in 1852, still keeping each other company 

 at the same distance apart as in 1846, but since then they 

 have never been seen again. Many other comets have been 

 discovered besides these, and it is probable that many thou- 

 sands or even millions must be wandering through space, 

 but of these we cannot speak here. 



Adams and Leverrier determine the Position of 

 an Unknown Planet by its Influence on the Orbit of 

 Uranus, 1843-1846. The next discovery which we must 

 consider is one of the most remarkable in the history of 

 astronomy, because it was not made with the telescope, but 

 was worked out independently by two men entirely by 

 means of Newton's theory of gravitation. You will remem- 

 ber that in 1781 Sir William Herschel discovered the planet 

 Uranus moving outside all the other planets (see p. 282). 

 Now, many astronomers had noticed this body in earlier 

 ages, and supposing it to be a star, had marked its position 

 from time to time in the heavens, and from these observa- 

 tions it was now possible to calculate its path round the sun. 

 When this was done it was found, however, that the planet 

 did not move as it ought to do according to the theory of 

 gravitation. The pull of the sun and the known planets 

 did not account for its orbit, for it roamed farther out into 



