THE PLANET NEPTUNE. 49 



distances are about 207 and 233 years. This conclusion 

 was unauthorized, and is now admitted by Le Verrier to 

 have been erroneous. The mean distance of Neptune 

 from the sun is only thirty times that of the earth, and 

 still it explains the motions of Uranus even better than 

 the hypothetical planet of Le Verrier. 



Professor Peirce has shown that an important change 

 in the character of the perturbations takes place near the 

 distance 35*3. A planet at the distance 35'3 would re- 

 volve about the sun in 210 years, which is exactly two 

 and a half times the period of the revolution of Uranus, 

 Now if the times of revolution of two planets were ex- 

 actly as 2 to 5, the effects of their mutual influence would 

 be peculiar and complicated. This distance of 35*3 is a 

 complete barrier to any logical deduction, and the invest- 

 igations with regard to the outer space can not be ex- 

 tended to the interior. 



The observed distance 30 belongs to a region which is 

 even more interesting in reference to Uranus than that of 

 35 '3. The time of revolution which corresponds to the 

 mean distance 30*4 is 168 years, being exactly double the 

 year of Uranus ; and the influence of a mass revolving in 

 this time would give rise to very singular and marked 

 irregularities in the motion of this planet. Professor 

 Peirce was hence led to the conclusion that the planet 

 Neptune was hot the planet to which geometrical analysis 

 had directed the telescope ; that its orbit was not contain- 

 ed within the limits of space explored by Adams and Le 



Verrier in searching for the source of the disturbances of 



3 



