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    Re: Old Sextant on German money
    From: Richard M Pisko
    Date: 2007 Mar 14, 11:28 -0700

    On Sat, 10 Mar 2007 10:32:39 -0700, George Huxtable
    > It may be worthwhile making the added mirror less than perfectly flat;
    > perhaps very slightly curved or rippled, so as to diffuse the
    > reflection a bit and relax the need for precise alignment.
    It is not necessary to do anything to the mirror as the light will cone
    outward at about a 16 minute angle anyway, and rough aperture sights work
    well enough for alignment.  Check Google for other designs of signalling
    and surveying heliographs; some will be listed under heliotrope.  The US
    Army, the US Geologic Survey, and the Coast and Geodetic Survey people
    used many interesting designs as targets on monuments for the first order
    triangulation networks and the secondary webs.  Some were manned, some
    used rotating mirrors; one of the most elegant to my eye was an array of
    curved, mirror-glass tubes.  The field expedient of coating the inside of
    a liquor bottle with a thin film of mercury worked if the knowledge and
    chemicals were available; but apparently they tended to be used as rifle
    targets in the Western states, and didn't last long.
    This site:  is dedicated to heliographs.
    shows the Gaussian heliotropes and the parallel, curved, mirrored tubes I
    Richard . . .
    Using Opera's e-mail client since Dialog, "the Dog", died.
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