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    Re: Newtons octant
    From: George Huxtable
    Date: 2007 Nov 15, 11:02 -0000

    There is some serious misunderstanding going on.
    
    Mike Daly questioned Ted Gerrard's account, and when challenged-
    
    "> So what Mike, made you think this engraving was a copy of Newton's own
    drawing?"
    
    replied-
    
    | I don't care how much the details of the drawing match the text, since
    | my comments are based on the text:
    |
    | "In the annexed Scheme, PQRS denotes a Plate of Brass..."
    
    =================
    
    That text came from a letter, stated to be in Newton's handwriting, found in
    the papers of Halley after his death. That letter itself hasn't survived,
    and neither has Newton's "annexed scheme", but the text of the letter was
    copied for the Royal Society by the finder, its vice-president Sir William
    Jones. I doubt if there's any dispute about the genuineness of the letter.
    We can take it at face value. But not the "annexed scheme", which doesn't
    exist, and presumably had to be imagined-up, 50 years later, at the Royal
    Society, for the ink-and wash drawing in RS Letters and Papers, 1742, vol 1,
    p.120 (a reference cited by Gerrard). So what did the artist of that drawing
    have to go on? As far as we know, only Newton's text, and no "attached
    scheme". No doubt, he interpreted that text as best he could, with the help
    of the experts of the day, but that doesn't make that drawing an authentic
    represention of what Newton's scheme would have been. And then, in another
    indirect process, that so-familiar engraving was made, presumably from that
    drawing. There are discrepancies to be found between those three documents,
    the letter, the drawing, and the engraving, which Ted Gerrard goes into,
    though I don't go along with Ted about the importance of every such detail.
    
    ======================
    
    In response to Ted's quote- |
    | "AB, is a Telescope, three or four Feet long, fixt on the Edge of that
    | Brass Plate."
    
    Mike asks-
    | So - why would someone willingly look forward to holding and taking
    | measurements using a triangle of brass with a 3-4 foot telescope on it?
    
    I'm not sure what point Mike is trying to make here. You have to make the
    best of what the technology of the day allows. Before the days of achromatic
    lenses, telescopes had to be long or they were bedevilled by chromatic
    aberration. Halley's own telescope, for observing Moon appulses, was longer
    still. How he managed to use it on board ship. I have no idea. Because the
    telescope had to be so long, it didn't necessarily follow that the brass
    triangle had to be the same size, though that's what the later Royal Society
    engraving implies. As discussed above, that engraving doesn't have to taken
    at face value.
    
    George.
    
    contact George Huxtable at george---.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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