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    Re: System Gago Coutinho
    From: Gary LaPook
    Date: 2010 Feb 15, 16:56 -0800

    Frank Reed wrote:
    > Gary, you wrote:
    > "I am attaching an excerpt from the book "Precision Astrolabe" that
    > describes the Coutinho sextant and other sextants adapted to aviation
    > use."
    > Thank you. That's a rather rare book. Copies on Abebooks.com are
    > selling for about $65 and up. Could I ask you to post pages 192-193?
    > They don't seem to have made it into your sextants.pdf file.
    > This book, as well as another which I found through google, stress
    > that the key feature that was novel at the time was that the Gago
    > Coutinho bubble horizon employed a spirit level which was curved in
    > just the right ratio so that if the sextant is pitched up and down
    > (rotated about an axis perpendicular to the sextant frame and passing
    > through the eye-end of the sighting tube or telescope) the image of
    > the Sun or star and the bubble remain together much the same as with
    > respect to the sea horizon in a standard marine sextant. This was
    > standard in later bubble sextants, but back then it was apparently a
    > big deal. Also, the diagrams in the pages you posted clear up one
    > other puzzle. In photos of his original prototype and also of the
    > production Plath versions, the housing for the bubble and the mirror
    > appear to be behind the mirrored part of the horizon glass, and we can
    > even see that the usual horizon shades are available for the clear
    > part of the horizon glass. The bubble housing does not block them (not
    > completely at least). According to the book, the horizon mirror of the
    > Gago Coutinho type of sextant was unique in that the horizon glass was
    > divided into three parts. Only a small central section was fully
    > mirrored. The section away from the frame was clear and allowed a view
    > of the sea horizon if available. The section near the frame was also
    > clear and allowed a clear view of the bubble. Of course, all three
    > sections could reflect the image of the celestial body.
    > -FER
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