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In response to my statement-

> I've never, to my recollection, even suggested that Halley used lunar
> distances. All his observations that I've examined have been of lunar
> appulses with stars, to determine the Moon's position, and have involved
> no
> measurement of lunar distance at all.

Mike Daly wrote-

| Of what use is Newton's instrument in occultations and appulses?  You
| just need a telescope.

Aha... The penny has dropped! I couldn't have put it better myself.

Though I tried. How I tried...

In Navlist  3870, I wrote-

" ...And not,
usually, an "occultation", but an "appulse" or near-miss, of the Moon as it
passed a star. As near as I could tell, he timed (relative to a star
time-sight) the moment when he judged the star to be aligned with an
extended line which joined the horns of the Moon. How he allowed for
parallax, I do not know. I've seen no mention, in Thrower, of any
measurement of lunar-distance that could be identified as such. That does
not imply that it didn't happen, however. Halley's method avoided the need
for a measure of lunar distance".

and in Navlist 3880, in response to his question-

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

I replied-

"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."

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

And that's the very point I've been trying to get across, but obviously
failed to do so. Newton developed the instrument in order to measure lunar
distances. But Halley didn't USE it to measure lunar distances! His "lunars"
were based on a method of his own devising, used by nobody else before or
since, and probably useful only to a skilled astronomer. As Mike Daly says,
it needed only a telescope. Newton, not having read Halley's journal (as we
can) thought, incorrectly, that Halley's longitudes resulted from using his
instrument.

Halley, we presume, used Newton's instrument to measure altitudes, for
getting latitude and for establishing local time. And that's why Ted Gerrard
relied on Halley's latitudes, and not his longitudes, to prove that he was
using an instrument that was very special for his time.

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

After a bit more research, I can offer some extra morsels.

I'm told that the text of the entry in the Journal Book, as quoted by
Gerrard, which is only found in a shortened form in many textbooks, appears
in full in Bruce Bauer's "The Sextant Handbook" of 1986. I'm sure many
members will have that book on their shelves (though I don't) and will be
able to confirm whether that is the case. If so, I would like to learn where
Bauer says it came from.

And again, I'm told that Halley wrote, in Phil. Trans. 37, (1731), 185-95,
that he obtained his longitudes at sea by observations of "a near Transite
of the Moon by a known fix'd star", using "a five or six foot telescope,
capable of showing the appulses or occultations of the Fix'd stars by the
Moon, on shipboard, in moderate weather." How he managed such a telescope, I
have no idea, but at a guess it must have been suspended from the rigging at
the far end. In Lecky's sexist words, a century lator, "sailors are not
women". Not in those days, they weren't.

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.

















|
| > It was written at the time as a formal official record of the Royal
Society
| > gathering by the Secretary appointed to do so, and subject to later
scrutiny
| > as being a true record. Hearsay? Absurd!
|
| Having attended many meetings of one royal society and one royal
| institute (neither in Britain), having been an executive of the first, I
| can assure you that secretaries make mistakes - that's why the first bit
| of the meetings is to review and correct the prior minutes.  And even
| after such corrections, there are still errors.  Further, the minutes
| are not completely written during the meetings; some are changed in the
| days, weeks or even months afterwards.  The text always contains the
| secretary's interpretation of what was said, not direct quotes.  I
| should note that this is with modern tape recording equipment available.
|
| I rather doubt that London's Royal Society of the day was somehow
superior.
|
| > Does he contend, then, that Newton didn't say what the Secretary wrote?
Or
| > that, for some reason, Newton was lying? Does Mike Daly know better,
then?
|
| I only know that the record does not give us specific knowledge of which
| instrument was used.  Nor does it specify the means by which Halley
| tested the instrument.  It does not quote Newton, but paraphrase him.
|
| > In a previous posting, he proposed instead, with no evidence whatever,
| > that Halley used an unworkable instrument of Halley's own design, but
| > suitably modified according to Daly's precepts (including a second
mirror)
| > to render it effective. Complete fantasy!
|
| You're making this up entirely.  I stated that the instrument would work
| - it may not be he best instrument ever, but it would work.  I then said
| that if _I_ were to make it, I'd suggest some modifications to make it
| more workable.  I also said that it could have been modified with a
| second mirror if you wanted it to be a double-reflection instrument.  I
| _never_ suggested that Halley actually used it, only that he could have
| if he wanted to.  There is no record on the matter one way or the other
| that I am aware of.  Cotter does not know of any either.
|
| Mike
|
|
| |
|
|
|
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|


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