CHAP. II., 5.] PHYSICAL ASTRONOMY. M. LEVERRIER MR ADAMS. 



33 



(141.) 

 Remarks 

 on the his- 

 tory. 



(142.) 



(144.) 



before it was at Berlin, M. Leverrier must still have 

 had a share in the credit of success. 



It is perhaps to be regretted that Mr Adams had 

 not given his whole investigation to the world, or 

 at least published his results, so as to avouch the 

 confidence which he felt in his own prediction, and 

 to throw upon practical astronomers generally the re- 

 sponsibility of its verification. Had he done so in 

 1845, it is possible that the planet might have been 

 discovered at the opposition of that year ; but it is at 

 least certain that M. Leverrier's claims to priority 

 as regards the discovery of Neptune would have 

 been effectually anticipated. But it is only just to our 

 countryman to recollect the difference of his age and 

 position. M. Leverrier was at the time about 35 

 years of age, and was a candidate for the sub- 

 stantial benefits as well as for the honour of a mem- 

 bership of the Academy of Sciences. Mr Adams 

 must have been nine or ten years younger at the 

 period of this discovery, a circumstance which en- 

 hances our admiraion at the achievement, whilst it 

 gives an additional grace to the modest conduct of 

 the author. 



I have endeavoured to state correctly (with due re- 

 gard to the limits of this essay) the main facts of the 

 most curious case of double discovery which, perhaps, 

 the history of science presents ; and happily as to the 

 facts, down to the minutest detail, no discrepancy of 

 opinion ever existed. Different minds will, with per- 

 fect truth, attach more or less distinction to the two 

 illustrious rivals, neither of whom has for an in- 



Theory Leverrier. 



1st Jan. 1847, 



318 47' 



36-15 



217'4 years 

 284 45' 

 0-1076 

 TfJw of Sun's 



Epoch of Elements, 



Mean Longitude, 



Mean Distance, 



Period, 



Long. Perihelion, 



Excentricity, 



Mass, . 



The differenpes of theory and observation are so 

 striking as to have occasioned surprise to many per- 

 sons that, with data so erroneous, the perturbations 

 of Uranus or the longitude of Neptune at the epoch 

 of discovery should have been obtained even approxi- 

 mately. 



(145.) The fact, however, is this : that the mutual per- 

 n as ~ turbations of Uranus and Neptune are sensible for 

 on ^7 a sma ll portion of the joint orbits when the 

 planets are nearly in conjunction. The conjunction 

 (when the mutual distance is least and the attraction 

 strongest) took place in 1822. Now the places of 

 Uranus from 1690 (the first observation) until 1800 

 can be sufficiently well represented by elliptic ele- 

 ments. The perturbation of Neptune became sen- 



sumption of 

 erroneous 

 elements 

 led to the 

 discovery 



stant lowered the dignity of his position by one 

 ungenerous expression, but that the absolute merit 

 of both is of the very highest character is on all 

 hands admitted. " The names of M. Leverrier and 

 Mr Adams," said Sir John Herschel, addressing the 

 Astronomical Society, " which Genius and Destiny 

 have joined, I shall by no means put asunder ; nor 

 will they ever be pronounced apart so long as lan- 

 guage shall celebrate the triumphs of Science in her 

 sublimest walks." 



But before closing, I must briefly state how far ( 143 -) 

 the orbit of the planet Neptune, when discovered, vati n S e f r " 

 realized the previsions of theory. A fortunate cir- Neptune as 

 cumstance rendered it easy to obtain at an early a fixed star, 

 period a correct knowledge of the elements. It seems 

 that the planet Neptune was observed by Lalande at 

 Paris on the 8th and 10th May 1795, and entered 

 as a fixed star, notwithstanding a distinct change of 

 place between the observations, actually corresponding 

 to what the planet should have had. 1 But such an 

 oversight had been made by Lemonnier in the case 

 of Uranus. By means of this observation of fifty 

 years back, the orbit was easily computed. It is a 

 singular and startling fact, that, except as regards the 

 longitude on the orbit, the other elements computed 

 from observation were somewhat widely different 

 from those assigned by M. Leverrier and Mr Adams. 

 We shall present them in a tabular view. The value 

 of the mass in the last column is calculated from the 

 elongation and period of a satellite of Neptune dis- 

 covered by Mr Lassell. 



Theory A dams . 

 6th Oct. 1846, 

 323 2 / 

 37'24 2 



299 11' 

 0-1206 



Observation Walker. 

 1st Jan. 1847. 

 328 33' 

 30-04 

 164-6 

 47 12' 

 0-00872 



sible therefore only twenty years before conjunction. 

 In this time Neptune describes (really) only ^ of a cir- 

 cumference, or 45, and relatively to the motion of 

 Uranus about the same. It is evident then that 

 even a considerable error in the period of Neptune 

 would scarcely sensibly affect the law of perturba- 

 tion during twenty years, and that the approximate 

 determination of the place of the perturbing planet 

 about the time of conjunction will not be much 

 affected by the error of that assumption. Again, 

 as to the error of mean distance, we may observe, 

 that since the mutual action of the planets is 

 confined within such (comparatively) narrow limits 

 of space and time, though we might anticipate a toler- 

 able approximation to the interval between the bodies 



1 One of the observations was suppressed in the publication, and only discovered on searching Lalande's MS. 



2 This was the hypothesis upon which Mr Adams made his second or corrected calculation of elements. Nevertheless, he 

 inferred from that calculation that the mean distance might with much probability be reduced to 33'4. 



3 Pierce. Struve's mass is 



