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    Re: Newton and Halley: was Re: the Shovell Disaster
    From: Michael Daly
    Date: 2007 Nov 15, 03:03 -0500

    George Huxtable wrote:
    
    > | If he did use lunar distances, it is often suggested that he used
    > | Newton's, which E.G.R. Taylor says was constructed by Thomas Heath and
    > | may have been shown in his shop window.
    >
    > Mike has that quite wrong. Where does Eva Taylor say that? In "The
    > Mathematical Practitioners of Tudor and Stuart England", her entry for Heath
    > says "He exhibited in his shop ... a quadrant on the principle of Hadley's
    > sextant which had been designed by Isaac Newton c. 1677 for finding lunar
    > distances". As Thomas Heath flourished in the period 1714-65, he was of
    > quite a different generation from Newton.
    
    In "The Haven Finding Art:...", she refers to a copy made by Heath.
    You're correct - I should have checked the dates - the instrument she's
    referring to couldn't have been made in time for Halley's use in the
    1690s.
    
    
    > He added-
    >
    > | However, I can't find much to
    > | support the claim that Halley used Newton's.
    >
    > 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".
    
    Unfortunately, those Journal Books are not online (anywhere that I've
    found).  I've read those bits in other sources.
    
    When I read that some time ago, it left me confused and looking for
    other sources of information.  "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.  It also doesn't state clearly that he found the longitude
    with it _at sea_.
    
    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?
    
    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.
    
    > I don't know that work of Cotter's, and would welcome a more detailed
    > citation, if it's in a journal.
    
    Charles H. Cotter, The Mariner's Sextant and the Royal Society; Notes
    and Records of the Royal Society of London, Vol. 33, No. 1 (Aug., 1978),
    pp. 23-36.
    
    I downloaded a pdf of this from the Royal Society web site.
    
    > But I have Cotter's "History of the
    > Navigator's Sextant", 1983, which shows Halley's "Instrument of Observing at
    > Sea" on page 109, and states that it was described to the Royal Society in
    > 1692. From Cotter's diagram, showing an instrument with a screw adjustment,
    > then if that's the same instrument, I can't see how it could possibly have
    > worked (but that doesn't prove that it couldn't). However, Cotter himself
    > concludes "There is no evidence that Halley's instrument was ever tested at
    > sea".
    
    That's no doubt the same diagram.  I can see it working, but I'd make a
    few minor changes.  The screw adjustment would need a fast adjustment
    mechanism, otherwise significant changes in angle would be tedious.  The
    folding telescope design is difficult to work with optically and I'd
    switch it with a short, straight scope with no lens at the top of the frame.
    
    The diagram makes it look like the diagonal element that crosses the
    screw is pinned at both ends - that is not right.  It has to slide at
    the upper end.  If you are familiar with the radio latino, that's
    basically the mechanism with a screw to set its size.
    http://en.wikipedia.org/wiki/Radio_latino
    
    Mike
    
    
    
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