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THE RETROSPECTIVE
CONSTRUCTION
OF HISTORY
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.
References:
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
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