"This memoir reached me about the 23rd or 24th of June. I cannot sufficiently express the feeling of delight and satisfaction which I received from it. The place which it assigned to the disturbing planet was the same, to one degree, as that given by Mr. Adams' calculations, which I had perused seven months earlier. To this time I had considered that there was still room for doubt of the accuracy of Mr. Adams' investigations; for I think that the results of algebraic and numerical computations, so long and so complicated as those of an inverse problem of perturbations, are liable to many risks of error in the details of the process: I know that there are important numerical errors in the _Mécanique Céleste_ of Laplace; in the _Théorie de la Lune_ of Plana; above all, in Bouvard's first tables of _Jupiter_ and _Saturn_; and to express it in a word, I have always considered the correctness of a distant mathematical result to be a subject rather of moral than of mathematical evidence. But now I felt no doubt of the accuracy of both calculations, as applied to the perturbation in longitude. I was, however, still desirous, as before, of learning whether the perturbation in radius vector was fully explained. I therefore addressed to M. Le Verrier the following letter:-- No. 13.--G. B. AIRY _to_ M. LE VERRIER. "'Royal Observatory, Greenwich, _1846, June 26_. [Sidenote: He puts the "radius-vector" question to Le Verrier, but makes no mention of Adams.] "'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 _Compte Rendu de l'Académie_ 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 tabular 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?'"