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    Re: Heath vernier sextant
    From: Alexandre Eremenko
    Date: 2012 Jul 23, 13:44 -0400

    Stan,
    
    > I have been playing in the sunlight (at least between the rain showers),
    > and the key, at least for me, seems to be getting the light source at the
    > correct angle with respect to the diffuser.
    
    Yes. Did you clean the arc and the vernier? I mean with a piece of
    slightly oiled cloth? Did you shift the microscope back and forth
    to achieve the maximum magnification?
    In most sextants I've seen the vernier is readable after you do this,
    in daylight, even if there are dense clouds.
    
    > BTW, what color LEDs did they use in 1940?
    
    They used an ordinary lamp. And long before that, they used an oil lamp.
    I've seen (photos of) several sextants (and repeating circles) of XIX century
    equipped with oil Lamps.
    
    By the way, I suppose that most of the observations in actual practice
    were made in daylight. Including Lunars.
    
    Lecky (late XIX century) strongly recommends sextants with large arc radius.
    Contrary to his recommendations, most of the sextants in XX century
    were made with relatively small arc radius of 6 1/2 or 7
    inches  (I suppose because of the frame
    rigidity considerations).
    
    I used to have a C. Plath circa 1911 with 10" vernier scale and 6 1/2 or 7
    inch radius, and reading it was a real pain:-)
    But the reason why I sold it was not that, but insufficient frame rigidity.
    
    I own a pocket sextant with scale of 2 1/2 inch radius, divided to
    1' with a vernier, and it is somewhat hard to read.
    
    Alex.
    
    
    
    
    
    

       
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