They Told The Story
A Neptune Chronology
Adams Dated Computations
The Forgotten Diary
Within One Degree
The Crown Jewels Document
Announcing The Discovery
Challis' Unseen Testimony
A Retrospective History
A Cantab. Clique
Adam's July Ephemeris
Mapless In Cambridge
Airy Tells the Truth
The Radius Vector: A Trivial Question?
Airy Blows His Top
Eggen Takes the Papers
Selected Correspondence
Primary Sources
Related Links.



To an alarming extent, the British story of Neptune’s co-prediction has relied on retrospective accounts, which the historical record prior to the discovery cannot corroborate. Let’s take some instances.

1) Airy’s address to the Board of Visitors, 29th June 1846.

‘On 1846 June 29th … the annual meeting of the Board of Visitors of the Royal Observatory Greenwich took place and among those present were Challis and Sir John Herschel. In a discussion on the benefits of international cooperation among astronomers, Airy … urged as an example of what he had in mind "the extreme probability of now discovering a new planet in a very short time," informing the Board of the close coincidence between Adams and Leverrier’s results derived from the hypothesis of a trans-Uranian planet.’ (Smart, p.59)

This is the standard tale, as created by Airy on November 13th, sterling evidence for how seriously the Brits had taken the planet-quest. It has hardly suffered alteration in the retelling, reappearing for example in Standage’s The Neptune File, (2000, p.92). It appears as the first occasion when Airy asked Challis about performing the sky-search.

This statement of Airy’s was cited by Smart (1947) as evidence over the extent to which Adams work was known before the discovery: ‘Nor were Airy and Challis alone in possession of knowledge of Adams work; the Board of Visitors were cognizant of it…’ (p.77) Let’s now turn to the record of what was discussed at that June 29th meeting, generally omitted in published accounts (although see Robert Smith 1989, p.412).

The Board of Visitors had been set up by Isaac Newton, President of the Royal Society, as an arrangement to keep an eye on Flamsteed, Britain’s first astronomer Royal, and as such had undertones of distrust. These seem to have faded away by Airy’s day, and all but two of its members were RAS fellows. The annual meeting was held on the 6th of June, the Board members being: Mr Babbage, Dr Peacock, Captain Beaufort, Dr Pearson, Prof. Challis Mr Sheepshanks, Prof Christie, Captain Smythe, Mr Johnson, Lord Wrottesley, Sir John Herschel, its Chair was the Marquis of Northampton. The Astronomer Royal was present ‘by request of the Board.’ Thus, the meeting in question was not that of the annual RGO report to the Board.

Airy gave his report (eleven pages as later published) of the RGO’s achievements in the past year. Minutes were read, instruments were checked, motions were put, votes were taken, and railway timetables were debated. Then on the 10th of June a Board of Admiralty meeting saw the same group assembled, hearing the minutes of the previous meeting. Then, because of a letter which Airy had sent to the first Lord of the Treasury, an ‘adjoined meeting’ was held on the 29th of June, and the same group turned up again at the Admiralty, with Airy’s letter having been circulated. In the context of international collaboration between observatories, Babbage moved that powers of the Board of Visitors be enlarged, and that Airy be co-opted onto the Board, for certain issues relating to this improved international collaboration - excluding their yearly checkup on the RGO. In other words, Airy summoning this extra meeting was a wheeze to give himself additional powers and presumably better summer holidays, by becoming partially co-opted onto the Board! The whole tone of the reports of these meetings is bureaucratic.

After the meeting, Airy may have conversed with Herschel on the subject of the two similar predictions, as he had written to William Whewell about some days earlier. Or, should we suppose that, over a glass of sherry, Airy enquired of Challis about conducting the sky-search at Cambridge? This was how Turner, quite reasonably saw things:
'Airy discussed the matter with Professor Challis... suggesting that he should immediately commence a search for the supposed planet at Cambridge.' (1904, p.63)

After all, Challis had succeded him as Cambridge’s Plumian Professor of Astronomy, so would they not have discussed the vital issue, once broached? But, this view is hardly compatible with the two letters sent by Airy to Challis, on July 9th and 13th, proposing to him the notion of conducting a sky-search.In these letters, Airy cautiously broaches the subject, in a way that makes it clear that the two have not previously discussed this issue. The first of these letters gave the reason:

‘I attach importance to the examination of that part of the heavens in which there is a possible shadow of reason for suspecting the existence of a planet external to Uranus.’

In his ‘Account’ of November 13th, Airy cited this letter, but deleted the words ‘a possible shadow of.’ Why should these words have been censored? The answer would seem to be, that he was at that meeting averring that he had affirmed before the Board on the 29th:

‘the extreme probability of now discovering a new planet in a very short time, provided the powers of one observatory could be directed to the search for it.’

- words highly incompatible with the censored phrase in the letter sent to Challis a week later. Airy's letter to Challis continued, after cautiously broaching the subject, 'Presuming that your answer would be in the negative ...' and he then offered to send an assitant by way of a bribe. The whole tone of this letter indicates that is is Airy's first mention of the subject to Challis. The letter was swiftly followed by another on the 12th taking a more urgent tone (see, "Correspondence").

Was Challis as a Board member startled to learn at that extra meeting, that he was to conduct a sky-search? It seems unlikely. The usual version of events derives from Airy’s Account given on November 13th (MRAS,54,p.400), whereby an ongoing discussion of international collaboration led Airy to his startling comments about the new planet which was expected to be discovered, citing both Adams and Leverrier’s results, and urging Challis to begin the search. Are we to believe that such a comment, as could not fail to become a main subject of conversation with so many astronomers present, would be unrecorded in the minutes?

The meeting as actually happened was summoned to discuss an improvement of international collaboration between observatories - while Airy’s plan, which he was then in the process of hatching, involved the opposite, a secret sky-search using Leverrier’s data without telling him! Had he spoken as he later claimed, Airy would have had to explain to an astonished Board why Greenwich would be having nothing to do with the sky-search, and why it ought to be conducted at Cambridge. Airy would have found that difficult, and it would have certainly ended up in the minutes. The historical record, which we ought rather to follow, involves the Board of Visitors only hearing about matters concerning the Greenwich Observatory.

Visitors of the Royal Observatory at Greenwich Minute Book, in Public Records Office Kew London ADM.190/4, pp.213-9, 220-4.
Report of the Astronomer Royal to the Board of Visitors June 6th, 1846, pp1-11, in: ‘Royal Observatory Greenwich Report of the Astronomer Royal 1836-68, RGO publication.

2) The BAAS Meeting at Southampton

Adams wrote to Airy on September 2nd, his letter concluding:
‘I have been thinking of drawing up a brief account of my investigation to present to the British Association.’

Did he? No account of events omits the story of Adams arriving a day late on September 15th 1846 to the BAAS meeting at Southampton, by when the physical-mathematical section was finished, and feeling disappointed. No-one at that Association meeting noticed a Cambridge mathematician and RAS fellow claiming to know where a new planet was to be found. Merely days before the discovery, when the scientists there present would have every inducement to remember him, none recalled being shown the manuscript of his intended talk, as would have been sterling evidence of his commitment. No such manuscript survives amongst his posthumous notes. Adams is his usual rather invisible self at just the time when we look for proof. The idea of his casually wandering up to the BAAS meeting without having registered to give an address may remind one of his similar ‘bad luck’ at turning up at Airy’s house the year before, having declined to make any appointment.

That BAAS meeting opened with Sir John Herschel making his valedictory address as President, about the discovery that year of a new planet. This was ‘Astraea,’ a new minor planet! The contents of the BAAS meeting were extensively reported in the Athanaeum, over four or five weeks following the meeting. Later, immediately following Neptune’s discovery – on October 1st, the day after he heard the news - Herschel wrote to the Athenaeum averring that his speech had alluded to the discovery of a minor planet, and then added:

' it has done more, - it has given us the probable prospects of the discovery of another. We see it as Columbus saw America from the shores of Spain. Its movements have been felt, trembling along the far-reaching line of our analysis, with a certainty hardly inferior to that of ocular demonstration.'

No paper reported this stirring phrase, but Herschel appealed ‘to all present whether they were not used.’ These epic words would have gloriously echoed his father’s great discovery. Did Herschel write them down as Airy claimed (Athenaeum, Nov 28th p.1221) ? The recent re-telling of the story by Tom Standage reaffirmed this: ‘Herschel was writing a speech to be delivered at the meeting of the British Association a few weeks later. He was inspired to write ...’ (p.93). Had he done this, his manuscript would have been a showcase piece of British evidence. Herschel would have had no need to appeal to persons present, as to whether he had said these words. The archives of this BAAS meeting (kept at Oxford, Bodlean library) are extensive, well over a hundred pages, and their records of the week-long BAAS meeting, a mere week before Neptune’s discovery, contained no hint of any trans-Uranian planet-quest.

Fortunately for us, an Irish correspondent of Herschel, a Mr John Stevelly of Belfast, was present and did confirm these words in a letter to Herschel of 8th October, 1846: ‘I have read with much interest your letter to The Athenaeum…I have no hesitation in saying that I remember the words most distinctly. I am much surprised that they were not reported for they fastened themselves more upon my imagination, and afforded me more matter for mental speculation then almost any other sentence you had uttered’ (see "Correspondence").

3) Seeing Neptune

On the evening of September 29th, six days after the planet’s discovery in Berlin, the reverend James Challis directed his assistant to write, ‘seems to have a disc’ beside what, he later heard, was Neptune. This is an irresistible twist to the story, told wherever it is re-narrated. All that Challis’s log-book actually contains beside that date is:

‘Last one seemed to have a disc’

with ‘last one’ crossed out, -as doesn’t sound nearly so good. The ‘blame’ which falls on Challis is often interpreted in terms of his failure to ‘reduce’ his data i.e. interpret what the stars were, when in front of him. Challis had the great advantage, that the Northumberland telescope he was using was equatorial and had a clock-drive which could be ‘locked on’ to any portion of the sky as he wished – in contrast with the Greenwich meridian-transit telescope, where the stars just passed by one’s line of observation.

The actual quote gives the impression of Challis vaguely recalling that the star just gone by looked bigger than the others, but not wanting to use the clock-drive to go back and inspect it. He was using far too high an enlargement, down to 11th magnitude (Neptune was 8th magnitude), so myriads of stars were passing continually across his line of sight.


Whewell Portrait, by permission of the Master & Fellows of Trinity College, Cambridge