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Mike Daly had written-

However, I can't find much to support the claim that Halley used Newton's
[angle-instrument].

In reply, I wrote-

Well, what I referred to were Newton's words, as recorded in the Royal
Society's Journal Book for 1699, when Newton referred to his instrument, in
Halley's presence, as having been used at sea by Halley. Halley was in
London, in the short interval between his two Atlantic voyages to survey
magnetic variation. Here is what the record states, on 16th August 1699-

"Mr Newton showed a new instrument contrived by him for observing the moon &
Starrs, the Longitude at Sea, being the old Instrument mended of some
 faults, with which notwithstanding Mr Hally had found the Longitude better
than the Seamen by other means".

Mike now replies-

| Unfortunately, those Journal Books are not online (anywhere that I've
found).  I've read those bits in other sources.

Is Mike claiming, then, that because they can't be found online, it puts
that record somehow in doubt?

| When I read that some time ago, it left me confused and looking for
| other sources of information.

Just because it leaves him confused, is that a reason to reject it? It seems
clear enough to me.

  "A new instrument" and "the old
| instrument corrected of some faults" suggest it might not be the
| original design, but an improved version or even an entirely new
| instrument.

Well, yes, that might well be the case. So what?

A plausible scenario might be this- Halley had taken the instrument to sea
for his first Atlantic voyage, and had found some problems, which needed
fixing, so he had returned the instrument to Newton at the Mint on his
return, only the previous month. Newton (or his crafttsmen at the Mint) had
promptly put those right, and reported to the Royal Society, acknowledging
those problems and improvements.

| It also doesn't state clearly that he found the longitude
| with it _at sea_.

My reading of it does. How else does he interpret the words "with which
notwithstanding Mr Hally had found the Longitude better than the Seamen by
other means"? However, we know better (or I think I do anyway) having the
advantage of reading Halley's journals which Newton would not have had, and
which show that his "lunars" came from a different method than lunar
distance. That's exactly why, in my original posting, I used Halley's
precise latitudes, rather than his longitudes, as evidence that he was
indeed using a two-mirror instrument. Newton's instrument would have been
used for his latitudes, and also for his star altitudes to get local time,
part of the process for finding longitude.

But Mike was disputing that Halley had taken Newton's instrument to sea, (or
disputing that Newton had said he had- I'm unsure which), not whether or not
he had used it to find the longitude.

| Another issue is that Halley commented, on seeing Hadley's new
| instrument, that Newton had previously designed such.  He later
| retracted that claim and said that Hadley's was unique.  If Halley had
| used Newton's instrument, how could he have forgotten so much about it
| that he could not stand by his initial statement?

Gerrard deals with that matter in some detail, and I suggest that Mike
consults his book before taking it further. He quotes Halley's words, at a
meeting of the Royal Society on 27 Dec 1731, as- "Dr Hadley took occasion to
say that he had considered the construction of Mr Hadley's new invented
instrument for making observations on board a ship and was now well
satisfied that it was much different from that which Sir Isaac Newton
formerly invented for that purpose &~ communicated to the Society".

Note that all Halley had conceded was that the two instruments were "much
different"; which they were, although they were clearly based on exactly the
same principle. Had he been "leant on", by Hadley and his supporters, in
order for Hadley to be able to claim a patent, which would otherwise have
been denied? I wonder, and so does Ted Gerrard.

| Halley never mentions which instruments he used.  I can't find any
| source that suggests that Newton's was used that doesn't just refer to
| the single document you cite.  That's what I meant when I said I can't
| find anything to support the view.  If a ship's log, officer's notes,
| Greenwich document, Halley's own writings etc had provided an
| independent identification of the instrument, I'd accept it.  Instead I
| find writers who put this in doubt.

WHO puts the matter in doubt, exactly? On what basis? What evidence can Mike
offer that Halley used some other instrument? What instrument would that be,
then? And how can he square the use of the known instruments of his day with
the precision of his latitude observations, made at sea, on the English
Channel coasts? To me, that's decisive.

================

Mike suggests that Halley's own proposed instrument of 7 years earlier, as
referred to by Cotter, may have been what he took to sea on those voyages.
But that was a single-reflecting device, with considerable angular motion
between horizon and celestial body as it's rocked, which addition of a
telescope would only worsen. It shared the same problems, used at sea, as
the cross-staff and backstaff, which a two-mirror intrument would eliminate
in a stroke.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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