SCIENTIFIC PREDICTION 189 



occasion of the investigation now undertaken. That 

 thirteen unknown quantities were involved indicates 

 sufficiently the difficulty of the problem. 



Adams started with the assumptions, not improb- 

 able, that the orbit of the unknown planet was a 

 circle, and that its distance from the sun was twice 

 that of Uranus. This latter assumption was in accord 

 with the so-called " Bode's Law," which taught that 

 a simple numerical relationship exists between the 

 planetary distances (4, 7, 10, 16, 28, 52, 100, 196), 

 and that the planets as they lie more remote from 

 the sun tend to be more nearly double the distance 

 of the next preceding. Adams was encouraged, by 

 his first attempt, to undertake a more precise de- 

 termination. 



On his behalf Professor Challis of Cambridge ap- 

 plied to Astronomer Royal Airy, who furnished the 

 Reductions of the Planetary Observations made at 

 Greenwich from 1750 till 1830. In his second en- 

 deavor Adams assumed that the unknown planet had 

 an elliptical orbit. He approached the solution grad- 

 ually, ever taking into account more terms of the per- 

 turbations. In September, 1845, he gave the results 

 to Challis, who wrote to Airy on the 22d of that 

 month that Adams sought an opportunity to submit 

 the solution personally to the Astronomer Royal. On 

 the 21st of October, 1845, the young mathematician, 

 twice disappointed in his attempt to meet Airy, left 

 at the Royal Observatory a paper containing the 

 elements of the new planet. The position assigned 

 to it was within about one degree of its actual place. 



On November 5 Airy wrote to Adams and, among 

 other things, inquired whether the solution obtained 



