* THE PLANET NEPTUNE. 45 



The following table shows the distance of the planet 

 from the sun, as predicted by Le Terrier, and that de- 

 duced from the computations of Mr. Walker, the dis- 

 tance being expressed in radii of the earth's orbit. 



Thus it appears, that during the 30 years in which 

 the action of Neptune upon Uranus has been sensible, 

 the error of the predicted distance from the sun has never 

 amounted to one tenth of the whole quantity. 



There appears, however, a discrepancy between the 

 limits of distance which Le Terrier assigned to his planet 

 before its discovery, and those which he has since pub- 

 lished. In 1846 he attempted to determine the limits 

 within which the distance might be supposed to vary 

 without involving an error greater than 5" in any of the 

 observations since 1781. He decided that the mean dis- 

 tance could not be less than 35*04, nor more than 37*90. 

 Now the mean distance of Neptune from the sun is 

 known to be only 30*04. From these two propositions 

 the legitimate conclusion would seem to be that Neptune 

 is not the planet predicted by Le Terrier. But Le Ter- 

 rier has lately changed his ground, and he has dis- 

 covered that without supposing the uncertainty of the 

 modern data to exceed 5", the theory of Uranus may be 

 satisfied by a planet situated in 1846 at any distance from 



