the Planet exterior to Uranus. 521 



For the modern observations I have used the method of nor 

 mal places, taking the mean of the tabular errors, as given by 

 observations near three consecutive oppositions, to correspond 

 with the mean of the times ; and the Greenwich observations 

 have been used down to 1830: since which the Cambridge 

 and Greenwich observations, and those given in the Astro- 

 nomische Nac/tricftten, have been made use of. The following 

 are the remaining errors of mean longitude : — 



Observation— Theory. 



» 



+ 0-30 

 + 1-92 

 -f-2-25 

 -1-06 

 -1-44 

 — 1-62 

 + 1-73 



The error for 1780 is concluded from that for 1781, given 

 by observation compared with those of four or five following 

 years, and also with Lemonnier's observations in 1769 and 

 1771. 



" For the ancient observations, the following are the re- 

 maining errors : — 



Observation — Theory. 



1690 +44-4 1750 — V6 1763 — 5 1 



1712 + 6-7 1753 +5-7 1769 + 0-6 



1715 — 68 1756 -40 1771 +118 



The errors are small, except for Flamsteed's observation of 

 1690. This being an isolated observation, very distant from 

 the rest, I thought it best not to use it in forming the equa- 

 tions of condition. It is not improbable, however, that this 

 error might be destroyed by a small change in the assumed 

 mean motion of the planet." 



I acknowledged the receipt of this paper in the following 

 terms: — 



No. 12. G. B. Airy to J. C. Adams, Esq. 



" Royal Observatory, Greenwich, 1845. Nov. 5. 



" I am very much obliged by the paper of results which you 

 left here a few days since, showing the perturbations on the 

 place of Uranus produced by a planet with certain assumed 

 elements. The latter numbers are all extremely satisfactory : 

 I am not enough acquainted with Flamsteed's observations 

 about 1690 to say whether they bear such an error, but I 

 think it extremely probable. 



" But I should be very glad to know whether this assumed 

 perturbation will explain the error of the radius vector of 



Phil. Mag. S. 3. No. 197. Suppl. Vol. 29. 2 N 



