Astronomy, or 121 



ence to the distance itself which is to be valued ? Whoever, in order to 

 strike the imagination of the public, should express this difference in 

 post-leagues, that is, referring it to the slowness with which we crawl 

 upon the surface of our globe, would be following a proceeding unwor- 

 thy of an astronomer. Now, in 1812 I have made an error of T ^th 

 of the distance, in 1822 and 1832 ^yi^andin 1842 T yh ; never the 



4 ^.^ J ] ___ 1*_1T*11 1 1 ■ ■ % • * * ■ 1 * 



tenth which I might have reached without being liable to any reproaches. 

 " The direction was more precise than the distance. This might be, 

 — for if the direction had been false, nothing could have compensated 

 for the error which would have resulted in the attraction of Neptune 

 upon Uranus. Whilst, if the planet be placed a little too far in a given 

 direction, the error, which would result in the quantity of attraction, 

 may be immediately destroyed by making the planet a little larger. 

 This is precisely what has taken place. I placed Neptune rather too 

 far ; but I made it rather too large. I might have placed it in any inter- 

 mediate place, even a little too near, provided I had made it a little too 

 small. But what am I saying? I have made Neptune too large ! I for- 

 got that this is a third objection. Let us examine it however. * 

 u Thirdly. — Is it true that the theoretic mass of Neptune differs from 

 the mass deduced from observations of the satellite, to such a degree as 

 to be an irresistible argument against the identity of the theoretic Nep- 

 tune with the observed Neptune ) NO ; this is false. Let us again have 

 recourse to figures. According to M. Struve the mass deduced from the 

 satellite is -^ of the mass I had predicted. But I will grant, if it is 

 insisted on, that -ffo must be taken ; which, however, is only arrived 

 at by choosing from among the different results obtained that which 

 leads to the greatest deviation. I declare that if any one should be 

 misled by this deduction, which corresponds only to a variation of a 

 fifth in the diameter of Neptune, it would only be by keeping out of 

 s *gbt the difficulties of the same kind presented by the masses of the 

 other planets. The mass of Uranus has been also determined by two 

 different methods — by the action of this planet upon Saturn, and by the 

 consideration of its satellites. Well, the second of the values thus de- 

 termined is only ^ of the first. And yet there were forty years 

 °f direct observation of Uranus at disposal whilst I had not a single ob- 

 servation of Neptune. And yet the mass only of Uranus was required 

 to be deduced from its perturbations on Saturn, whilst I sought, from 

 those of Neptune on Uranus, the direction, the distance, and the mass 

 of the planet. Will it be said then that there are two planets Uranus? 

 « should, to be consistent. Thus, then, the direction, the distance from 

 th e Sun, the mass of Neptune — that is to say, the only three things 

 which might justly be required — are exact in my theory beyond all 

 hope. The Neptune which has been found, like that which I sought, 







satisfies perfectly the perturbations of Uranus. This great accusation 

 *frich has made so much noise, falls back into that nothingness from 

 which it ought never to have emerged. I might stop here. A few 

 roore words, however, to show how the public is abused by pretended 

 enormous unheard-of errors held up to it. Around the principal star y 

 Virginis, and under the influence of its action, revolves another star to 

 Jhbh observations, made from 1718 till 18:?5, an interval of 117 years, 

 had assigned a certain elliptical orbit. Ten years of new observations 



Sicond Series, Vol. VII, No. 19.— Jan., 1849. 16 





