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    Re: The lost expedition of La Perouse
    From: Alexandre Eremenko
    Date: 2005 Jun 8, 15:10 -0500

    George,
    Do you know by chance when exactly and who
    made micrometer drum common?
    (I suspect that this could be Heath of London
    sometimes in 1930-s. Maybe you know more precisely?)
    In fact, micrometer drum was proposed in XVIII century
    possibly by Halley or even earlier. I can check when I
    come back to the US in August and will have access to my
    papers. I am curious why this invention had to wait until
    1930-s to become common.
    The reason is unlikely to be in some advanced wormscrew
    technology because a wormscrew was used in the arc
    division machines since XVIII century. So why did not they use
    it in sextants if the idea was known and technology available?
    Alex.
    
    On Wed, 8 Jun 2005, George Huxtable wrote:
    
    > What you would notice first is that there was no micrometer drum. Just a
    > fine-ajustment screw, but then you had to read the angle directly off the
    > engraved arc, with the help of a Vernier scale and a magnifying lens.
    >
    > You would find a longer telescope with smaller mirrors and a more
    > restricted field of view. Somewhat heavier, being larger than a modern
    > instrument, and made of brass, not aluminium.
    >
    > But otherwise, you could pick up an eighteenth-century sextant, and hardly
    > notice the difference between that and your own.
    >
    > For further information, I recommend "Taking the Stars", by listmember
    > Peter Ifland, beautifully illustrated.
    >
    >
    >
    > ================================================================
    > 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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