514- Prof. G. B. Airy on the History of the Discovery of 



modern observations suggested to me the possibility of some 

 disturbing body beyond Uranus, not taken into account be- 

 cause unknown. My first idea was to ascertain some approxi- 

 mate place of this supposed body empirically, and then with 

 my large reflector set to work to examine all the minute stars 

 thereabouts : but I found myself totally inadequate to the 

 former part of the task. If I could have done it formerly, it 

 was beyond me now, even supposing I had the time, which 

 was not the case. I therefore relinquished the matter alto- 

 gether, but subsequently, in conversation with Bouvard, I 

 inquired if the above might not be the case: his answer was 

 that, as might have been expected, it had occurred to him, 

 and some correspondence had taken place between Hansen 

 and himself respecting it. Hansen's opinion was, that one 

 disturbing body would not satisfy the phsenomena, but that he 

 conjectured there were two planets beyond Uranus. Upon 

 my speaking of obtaining the places empirically, and then 

 sweeping closely for the bodies, he fully acquiesced in the pro- 

 priety of it, intimating that the previous calculations would be 

 more laborious than difficult; that if he had leisure he would 

 undertake them and transmit the results to me, as the basis 

 of a very close and accurate sweep. I have not heard from 

 him since on the subject, and have been too ill to write. 

 What is your opinion on the subject ? If you consider the 

 idea as possible, can you give me the limits roughly between 

 which this body or those bodies may probably be found during 

 the ensuing winter? As we might expect an eccentricity 

 [inclination ?] approaching rather to that of the old planets 

 than of the new, the breadth of the zone to be examined will 

 be comparatively inconsiderable. I may be wrong, but I am 

 disposed to think that, such is the perfection of my equatorial's 

 object-glass, I could distinguish almost at once the difference 

 of light of a small planet and a star. My plan of proceeding, 

 however, would be very different: I should accurately map 

 the whole space within the required limits, down to the mi- 

 nutest star I could discern ; the interval of a single week would 

 then enable me to ascertain any change. If the whole of this 

 matter do not appear to you a chimera, which, until my con- 

 versation with Bouvard, I was afraid it might, I shall be very 

 glad of any sort of hint respecting it." 



My answer was in the following terms : — 



No. 2. G. B. Airy to the Rev. T. J. Hussey. 

 [extract.] 



" Observatory, Cambridge, 1834, Nov. 23. 

 " I have often thought of the irregularity of Uranus, and 



