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    Re: The repeating reflecting circle.
    From: George Huxtable
    Date: 2005 Jan 19, 12:13 +0000

    Thanks to Alex for countering my speculation, that Simms' book might have
    been referring to a different sort of dip. Clearly, it wasn't.
    
    He sais-
    
    >I site the history of the dipmeter from Simms book:
    >
    >"When the late professor Vince was engaged in making
    >observations upon extraordinary refraction in Ramsgate,
    >Mr Throughton contrived and constructed for his
    >use an instrument which he
    >called a Refraction-Sector.
    >
    >About five years afterwards, when preparations were making for
    >the first of the late North Polar Expeditions,
    >Mr Troughton was applied to by the late Dr Wollaston,
    >to make him an instrument on the principle of back observation
    >with the quadrant, to send with the expedition, to measure
    >the dip of the horizon; but upon Mr Troughton's producing his
    >Refraction-Sector, which was as well adapted to Dr. Wollaston's
    >purpose as that for which it was devised,
    >the Doctor immediately ordered
    >one to be made for him, and named it a Dip-Sector.....
    
    =============
    
    That's interesting. Barrow, at the Admiralty, in the mid-19th century, was
    sending expeditions (especially naval ones) off around the World,
    particularly to Polar areas.
    
    Wollaston was a physicist specialising in optics. I remember the name, but
    not the purpose, unfortunately (birefraction?) of the "Wollaston prism",
    from my schooldays.
    Barrow put the provision of instruments into Wollaston's hands.
    
    As a result there are many natural geographic features, particularly Arctic
    / Antarctic ones, named after Wollaston. Perhaps the explorers were
    particularly grateful for well-chosen instruments. More likely, on such
    voyages of discovery, they simply ran out of names, after using up their
    wives' names, and the Admiralty Commisioners' names, and perhaps a sponsor
    or two, Yes, even then, sponsorship paid off: for example, Boothia
    peninsula, in the Arctic, was closely related to Booth's Dry Gin. But I
    digress.
    
    As I understand it, temperature gradients above the horizon can be
    particularly strong and stable in the Arctic / Antarctic. I have read an
    account of a sledge expedition, trudging over what turned out to be a
    perfectly flat plain, in which it appeared that they were forever in the
    bottom of a shallow bowl, with the horizon appearing to slope upwards in
    all directions; very apparent to the naked eye, and rather disheartening.
    So a dipmeter could well have been an important item to Arctic travellers,
    and perhaps to the Soviet Arctic fleet.
    
    It will be interesting to learn about the Troughton refraction-sector.
    Rather then measure front and back horizons, as is done with a quadrant
    fitted for back-observation, and capable of looking over the observer's
    head, I wonder if instead it measured the vertical angle between two views
    of the horizon, to the observer's left and right.
    
    George.
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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