Neptune's Discovery: The British Case for Co-Prediction, By Nick Kollerstrom

On October 17th, some weeks after Neptune’s discovery, the Reverend James Challis claimed in The Athenaeum that:

‘In September, 1845, Mr. Adams communicated to me values which he had obtained for the heliocentric longitude, excentricity of orbit, longitude of perihelion, and mass, of an assumed exterior planet - deduced entirely from unaccounted-for perturbations of Uranus’ (p.1069)

Challis repeated this at the November 13th RAS meeting, still without saying what the values were, and then reaffirmed it again at his Report to the Cambridge Observatory Syndicate on December 12th, still without showing it or declaring any of its values. Adams himself emphasized its importance at his (highly impressive) November 13th speech. After years of solitary toil, there at last came the great moment when: ‘I communicated to Professor Challis, in September 1845, the final values which I had obtained for the mass ...’, etc. of the assumed planet. Are we to believe that these ‘final values’ of Adams’ Herculean labours, as handed to his close friend and colleague, the top Cambridge astronomer, were of so little interest that no-one asked what they were?

No such document was ever published, nor did anyone record having seen it or having Challis tell them about its values. We are so familiar with the official story as has been told and re-told, of a past reconstructed from post-discovery statements, that it takes an effort to look with fresh eyes. On September 22nd 1845, Challis wrote to Airy saying

‘My friend Mr Adams (who will probably deliver this note to you) has completed his calculations respecting the perturbation of the orbit of Uranus by a supposed outer planet and has arrived at results, which he would be glad to communicate with you personally.’
Challis has got to hear about some results, but doesn’t claim to have any written set of orbital-elements. Adams needs someone to talk to about his work, preferably the Astronomer Royal, and is not quite ready at this stage to send a letter to anyone.

When next year he hears about the discovery, Challis writes off to the local newspaper Cambridge Chronicle on October 1st, and it is clear that he then had no memory of any such document (see "Announcing The Discovery"). Adams and Leverrier had, he wrote, both stumbled upon the result four months ago. That published statement is from the person doing the sky- search. Then he writes to Leverrier on the 5th, clearly with no memory of having been given an Adams prediction-document thirteen months earlier. Only two weeks later, does the official story take shape, with the above-quoted remark to The Athenaeum.

In 1901 when the main characters are all dead, Prof. Sampson, combing through Adams notes, finds an undated and unaddressed scrap of paper with some results on, and concludes:

‘It is very likely the above sheet is a copy of the communication Adams sent to Challis’(1904, MRAS, p.166)

This document had the month and year but no day written on it, in another’s hand presumably, Challis’. One is reminded of the bit of paper which Airy claimed to have received some weeks later than Challis, in October, which was likewise found to have the month and year but no day written on the top in another’s hand. Considering that these are supposed to be the two most important documents ever written by Adams, on which rests his claim to immortality, this seems rather peculiar.

In his October 17th letter above-quoted, following Neptune’s discovery, Challis added that: ‘The same results, somewhat corrected, he communicated in October to the Astronomer Royal.’ Adams on November 13th used a notably similar phrase: ‘The same results, slightly corrected, I communicated in the following month to the Astronomer Royal.’ (MRAS 54, p.429).

If either statement is valid, the document found by Sampson in 1901 cannot be the correct one - because all of its parameters are different. The eccentricity, the apse position, the helio longitude, the mass ... they come from two quite different computations. All they have in common, is their mean radius at the Bode’s-law orbit. Let’s look at them:

	Challis’ ‘Sept ’45’ document	Airy’s ‘Oct ’45’ document
Eccentricity	0.14	0.16
Apse position	320º	316º
Mean Helio long.	321º 40’	323º 34’
(at end of Sept ’45)

These are very high eccentricities (tenfold that of Earth’s orbit, which is 0.016) and his later ‘Hyp II’ of September ’46 reduced the value to 0.12. He put his planet close to perihelion (nearest approach), which means that, had he pushed this value up substantially between September and October, the planet’s distance would have been much diminished as would have had profound ramifications on his perturbation-terms ... they would all have had to be redone. There is no way that could be called ‘a slight adjustment’, nor could his work be described as ‘finished’ were so large a change made to his results, within weeks.

Although this document was never shown (that we know of), or its parameters specified, Challis did specify a phrase contained in it, when addressing the Cambridge Syndicate on December 12th . The paper gave, he explained, certain parameters: ‘... of the supposed disturbing planet, which he [Adams] calls by anticipation ‘The New Planet,’ evidently showing the conviction in his own mind of the reality of its existence.’ (SP of JCA, 1 p.l)

The document (here reproduced) supposedly given to the Astronomer Royal in September 1845 concludes with the stirring words ‘of the new planet’ (see "The Crown Jewels Document). Had the 27-year old Adams also boldly placed into the hands of the Plumean Professor of Astronomy a document about ‘The New Planet?’ The page later located by Sampson in 1901 lacked any such phrase, alluding merely to perturbations as could be explained ‘by supposing the existence of a more distant planet.’

Which doesn’t sound so good. Summarising, the document which Challis claimed to possess was rather lacking in manifest form or content. And yet, the document picked out by Sampson does tie up with the solution Adams obtained, dated September 18th.

Adams solution of -50? 34' which he reached on September 18th 1845 (see "Adams Dated Computations") is adjusted to -50? 3' a few pages later (Sampson 1904 p.166), and represents the angular distance between his mean UR and 'Neptune' values at his chosen epoch. This he defined as the mean-Uranus' solar opposition on 3rd May, 1810, and his calculations were all arbitrarily centred on this epoch-value. From then to 1st Oct. 1845 was 35 Uranus 'synodic' years, one of which equalled 1.10205 years. Thus his later date of 1st Oct. 1845 was likewise a mean-UR solar opposition (which differs from UR's actual solar opposition). What he calls 'longitude of Uranus at epoch' was 217.8? (Sampson p.160) and let's just accept this (That's the position of his mean UR, not the actual).

His 'Neptune' at 38.4 AU had an orbit-period of 237.6 years, and so moved 53° 40' in the given interval. So, to find his predicted mean-position from his notebook solution one adds these three together:

which compares well with the solution given on the 'Sampson's conjecture' note of 321° 40' (Adams has forgotten a half-degree term here due to precession, required because orbit-parameters are in sidereal space whereas zodiac longitude is tropical; his 'Hyp.II' computation done the next September included this).

His apse position was within a degree of this, implying that his true helio longitude will have more or less the same value. Adams' text gives a geocentric longitude, which is within three degrees of the then-correct value (323° 28'). This is no doubt impressive, but would not have found the planet.