34 ROUGH WAYS MADE SMOOTH. 



But still stranger and more impressive is the thought that 

 from researches such as these, Astronomy should be able to 

 infer the existence of a planet a thousand million miles 

 further away than Uranus itself. How amazing it would 

 have seemed to Flamsteed, for example, if on that winter 

 evening in 1693, when he first observed Uranus, he had been 

 told that the orb which he was entering in his lists as a star 

 of the sixth magnitude was not a star at all, and that the 

 observation he was then making would help astronomers a 

 century and a half later to discover an orb a hundred times 

 larger than the earth, and travelling thirty times farther away 

 from the sun. 



Even more surprising, however, than any of the incidents 

 which preceded the discovery of Neptune was this achieve- 

 ment itself. That a planet so remote as to be quite invisible 

 to the naked eye, never approaching our own earth within 

 less than twenty-six hundred millions of miles, never even 

 approaching Uranus within less than nine hundred and fifty 

 millions of miles, should be detected by means of those par- 

 ticular perturbations (among many others) which it produced 

 upon a planet not yet known for three-quarters of a century, 

 seemed indeed surprising. Yet even this was not all. As 

 if to turn a wonderful achievement into a miracle of com- 

 bined skill and good fortune, came the announcement that, 

 after all, the planet discovered in the spot to which Adams 

 and Leverrier pointed was not the planet of their calcula- 

 tions, but travelled in an orbit four or five hundred millions 

 of miles nearer to the sun than the orbit which had been as- 

 signed to the unknown body. Many were led to suppose that 

 nothing but a most marvellous accident had rewarded with 

 such singular success the calculations of Adams and Leverrier. 

 Others were even more surprised to learn that the new 

 planet departed strangely from the law of distances which 

 all the other planets of the solar system seemed to obey. 

 For according to that law (called Bode's law) the distance 

 of Neptune, instead of being about thirty times, should 

 have been thirty-nine times the earth's distance from the sun. 



