the Planet exterior to Uranus. 5 1 7 



I am engaged upon a general reduction of the observations of 

 planets made at Greenwich, from the commencement of Brad- 

 ley's observations to the present time. It may perhaps be a 

 year before I can furnish you with the places deduced from 

 these observations. * * * With respect to the errors of 

 the tables of Uranus, I think you will find that it is the lon- 

 gitude which is most defective, and that the errors in latitude 

 are not at present increasing. To show this, I set down a 

 few of my results. * * * You will see by this statement 

 that the errors of longitude are increasing with fearful ra- 

 pidity, while those of latitude are nearly stationary. * * * 

 I cannot conjecture what is the cause of these errors, but I 

 am inclined, in the first instance, to ascribe them to some 

 error in the perturbations. There is no error in the pure 

 elliptic theory (as I found by examination some time ago). 

 If it be the effect of any unseen body, it will be nearly im- 

 possible ever to find out its place." 



On the 24th of February, 1838, I addressed a letter to M. 

 Schumacher, which is printed in the Astronomische Nachri'ch- 

 ten, No. 349. In this letter it is shown, by treatment of the 

 results of the reduced observations of 1833, 1834, 1835, 1836 

 (to which allusion was made in my letter to M. Eugene Bou- 

 vard), that the tabular radius vector of Uranus was consider- 

 ably too small. This deduction (which has been confirmed 

 by the observations of all the subsequent years) has always 

 appeared to me to be very important. It is perhaps worth 

 while here to point out that the detection of this error arose, 

 in the first place, from the circumstance that my observations 

 of Uranus had not been confined to the mere opposition (as 

 had too often been done), but had been extended, as far as 

 possible, to quadratures; and, in the next place, from my 

 having so reduced the observations as to exhibit the effect of 

 error of the radius vector. 



On the 14th of May, 1838, I transmitted to M. Eugene 

 Bouvard the reduced observations of 1833, 1834, 1835, 1836; 

 and referred him to the paper in the Astronomische Nachrich- 

 ten, which I have cited. 



The following letter from M. Eugene Bouvard will show 

 how vigorously the attention of the astronomers of Paris was 

 still directed to Uranus: — 



No. 5. M. Eugene Bouvard to G. B. Airy. 

 [extract.] 



"Paris, ce21 Mai, 1844. 

 tt # * * Je viens aujourd'hui vous prier de me communi- 

 quer, si c'est possible, Ies ascensions droites et les declinaisons 



