the Planet exterior to Uranus. 513 



age, I have not directly contributed either to the theoretical 

 or to the observing parts of the discovery. In a matter of 

 this delicacy I have thought it best to act on my own judge- 

 ment, without consulting any other person ; I have, however, 

 solicited the permission of my English correspondents for the 

 publication of letters. 



Without pretending to fix upon a time when the conviction 

 of the irreconcilability of the motions of Uranus with the law 

 of gravitation first fixed itself in the minds of some individuals, 

 we may without hesitation date the general belief in this irre- 

 concilability from the publication of M. Alexis Bouvard's 

 Tables of Uranus in 1821. It was fully shown in the intro- 

 duction to the tables, that when every correction for pertur- 

 bation indicated by the best existing theories was applied, it 

 was still impossible to reconcile the observations of Flamsteed, 

 Lemonnier, Bradley and Mayer, with the orbit required by 

 the observations made after 1781, and the elements of the 

 orbit were adopted from the latter observations, leaving the 

 discordances with the former (amounting sometimes to three 

 minutes of arc) for future explanation. 



The orbit thus adopted represented pretty well the obser- 

 vations made in the years immediately following the publica- 

 tion of the tables. But in five or six years the discordance 

 again growing up became so great that it could not escape no- 

 tice. A small error was shown by the Kremsmiinster Obser- 

 vations of 1825 and 1826: but perhaps I am not in error in 

 stating that the discordance was first prominently exhibited 

 in the Cambridge Observations, the publication of which from 

 1828 was conducted under my superintendence. 



While still residing at Cambridge, I received from the Rev. 

 T. J. Hussey (now Dr. Hussey) a letter, of which the follow- 

 ing is an extract. It will be considered, I think, as honour- 

 able to that gentleman's acuteness and zeal. I must premise 

 that the writer had lately passed through Paris. 



No. 1 . The Rev. T. J. Hussey to G. B. Airy. 

 [Extract.] 



" Hayes, Kent, 17 November 1834. 

 " With M. Alexis Bouvard I had some conversation upon 

 a subject I had often meditated, which will probably interest 

 you, and your opinion may determine mine. Having taken 

 great pains last year with some observations of Uranus, I was 

 led to examine closely Bouvard's tables of that planet. The 

 apparently inexplicable discrepancies between the ancient and 



