CH. xxxi. DISCOVERY OF NEPTUNE. 293 



its orbit, for it roamed farther out into space than it should 

 do if they were the only bodies which attracted it. Either, 

 therefore, the early astronomers had marked the position of 

 the planet wrongly, or some unknown and unseen body 

 must be pulling it out of its course. This last seemed the 

 most likely explanation, but no such planet could be seen, 

 and the problem remained unsolved. 



It was at this point that a young student of St. John's 

 College, Cambridge, named John Couch Adams, then only 

 twenty-three years of age, made a memorandum in his note- 

 book to work out the movements of Uranus, and see if by 

 this means he could discover whether there was another 

 planet farther away from the sun. As soon as he had taken 

 his degree as Senior Wrangler in 1843, ne set to work to 

 carry out his intention, and two years afterwards he sent a 

 paper to Mr. Airy, the Astronomer-Royal at Greenwich, 

 stating in what part of the heavens astronomers ought to 

 look for the unknown planet which would explain the 

 capricious movements of Uranus. 



It is not easy for any but mathematicians to understand 

 what a wonderful thing it was to calculate accurately, in this 

 way, where a planet would be found which had never been 

 seen. When Pallas was discovered between Mars and Jupi- 

 ter, Piazzi saw it through the telescope for some days, and 

 it was only found again by following out the movement 

 which he had recorded. But in Adams's case nothing had 

 ever been seen, and the only reason for suspecting anything 

 to be there, was that astronomers could not make their very 

 difficult calculations of the attraction of the different planets 

 come out right. Adams, therefore, had first to calculate all 

 the attractions of the sun and the planets, in their different 

 positions, and then to find out how they would affect Uranus 



