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



No. 13. G. B. Airy to M. Le Verrier. 



"Royal Observatory, Greenwich, 1846, June 26. 



" I have read, with very great interest, the account of your 

 investigations on the probable place of a planet disturbing the 

 motions of Uranus, which is contained in the Comptes llendus 

 de V Academic of June 1 ; and I now beg leave to trouble you 

 with the following question. It appears from all the later 

 observations of Uranus made at Greenwich (which are most 

 completely reduced in the Greenwich Observations of each 

 year, so as to exhibit the effect of an error either in the ta- 

 bular heliocentric longitude, or the tabular radius vector), 

 that the tabular radius vector is considerably too small. And 

 I wish to inquire of you whether this would be a consequence 

 of the disturbance produced by an exterior planet, now in the 

 position which you have indicated. 



" I imagine that it would not be so, because the prin- 

 cipal term of the inequality would probably be analogous to 

 the moon's variation, or would depend on sin 2 (v— u) ; and 

 in that case the perturbation in radius vector would have the 

 sign — for the present relative position of the planet and 

 Uranus. But this analogy is worth little, until it is supported 

 by proper symbolical computations. 



" By the earliest opportunity I shall have the honour of 

 transmitting to you a copy of the Planetary Reductions, in 

 which you will find all the observations made at Greenwich 

 to 1830 carefully reduced and compared with the tables." 



Before I could receive M. Le Verrier's answer, a transac- 

 tion occurred which had some influence on the conduct of 

 English astronomers. 



On the 29th of June a meeting of the Board of Visitors of 

 the Royal Observatory of Greenwich was held, for the con- 

 sideration of special business. At this meeting Sir J. Her- 

 schel and Professor Challis (among other members of the 

 Board) were present ; I was also present by invitation of the 

 Board. The discussion led, incidentally, to the general ques- 

 tion of the advantage of distributing subjects of observation 

 among different observatories. I spoke strongly in favour of 

 such distribution ; and I produced, as an instance, the extreme 

 probability of now discovering a new planet in a very short 

 time, provided the powers of one observatory could be directed 

 to the search for it. I gave, as the reason upon which this 

 probability was based, the very close coincidence between the 

 results of Mr. Adams's and M. Le Verrier's investigations of 

 the place of the supposed planet disturbing Uranus. I am 

 authorized by Sir J. Herschel's printed statement in the 



