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    Re: Sextant and quintant limitst: was: sextants on aeroplanes
    From: Richard M Pisko
    Date: 2008 Dec 19, 23:27 -0700

    On Sun, 14 Dec 2008 03:41:37 -0700, George Huxtable   
    wrote:
    
    > However, it seems to me at least plausible for a 2-mirror instrument  
    > (which
    > couldn't, any longer, be called a sextant) to be designed, which could
    > measure angles from zero to 180º, though nobody ever seems to have done  
    > so.
    > That's material for another posting.
    
    George,
    
    You might take a look at this instrument from the Smithsonian (National  
    Museum of American History)  Physical Sciences Collection - Surveying and  
    Geodesy; Alidade (reflecting) by G. Dolland PH*319452: (see 35 KB  
    attachment)
    
    The mechanism is such that the angle between the rule edge and the  
    adjusting (index) arm edge is the same as that between the line of sight  
    through the aperature over the "horizon" mirror to the first object, and  
    the reflected line of sight to the second object.  This is set around 25  
    degrees, I think.
    
    There is a very similar instrument in (if I recall correctly) in one of  
    the British museums; opened to a wider angle, close to 60 degrees.
    
    I have not been able to find out what the inventor called the various  
    parts, but I hope you can follow my description while looking at the  
    illustration.
    
    -- 
    Richard . . .
    
    Using Opera 9.2.4 after the "Dog" died
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