522 Prof. G. B. Airy on the History of the Discovery of 



Uranus. This error is now very considerable, as you will be 

 able to ascertain by comparing the normal equations, given in 

 the Greenwich observations for each year, for the times before 

 opposition with the times after opposition." 



I have before stated, that I considered the establishment of 

 this error of the radius vector of Uranus to be a very import- 

 ant determination. I therefore considered that the trial, whe- 

 ther the error of radius vector would be explained by the same 

 theory which explained the error of longitude, would be truly 

 an expcrimcntum crucis. And I waited with much anxiety for 

 Mr. Adams's answer to my query. Had it been in the affirma- 

 tive, I should at once have exerted all the influence which I 

 might possess, either directly or indirectly, through my friend 

 Professor Challis, to procure the publication of Mr. Adams's 

 theory*. 



From some cause with which I am unacquainted, probably 

 an accidental one, I received no immediate answer to this in- 

 quiry. I regret this deeply, for many reasons. 



While I was expecting more complete information on Mr. 

 Adams's theory, the results of a new and most important in- 

 vestigation reached me from another quarter. In the Comptes 

 Rcndus of the French Academy for the 10th of November, 

 1845, which arrived in this country in December, there is a 

 paper by M. Le Verrier on the perturbations of Uranus pro- 

 duced by Jupiter and Saturn, and on the errors in the ellip- 

 tic elements of Uranus, consequent on the use of erroneous 

 perturbations in the treatment of the observations. It is im- 

 possible for me here to enter into details as to the conclusions 

 of this valuable memoir: I shall only say that, while the cor- 

 rectness of the former theories, as far as they went, was gene- 

 rally established, many small terms were added ; that the ac- 

 curacy of the calculations was established by duplicate inves- 

 tigations, following different courses, and executed with ex- 

 traordinary labour ; that the corrections to the elements, pro- 

 duced by treating the former observations with these corrected 

 perturbations, were obtained ; and that the correction to the 

 ephemeris for the present time, produced by the introduction 

 of the new perturbations and the new elements, was investi- 

 gated, and found to be incapable of explaining the observed 

 irregularity of Uranus. Perhaps it may be truly said that 

 the theory of Uranus was now, for the first time, placed on a 

 satisfactory foundation. This important labour, as M. Le Ver- 

 rier states, was undertaken at the urgent request of M. Arago. 



In the Comptes Rendus for June 1, J 846, M. Le Verrier gave 



* Here the Astronomer Royal explained to the meeting, by means of a 

 diagram, the nature of the errors of the tabular radius vector. 



