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    Re: Bris Sextant
    From: Alexandre Eremenko
    Date: 2005 Nov 6, 20:42 -0500

    John,
    Thank you for your interesting observations.
    (I infer that you live on a sea shore, so I envy you:-)
    When you have time and good weather to
    to graduate the scale of your Bris, please
    inform us, I am interested in the precision you obtain.
    
    > I then held the apparatus in front of one side of a 7 x 35 binocular.
    
    As I said before, this is dangerous!
    
    > But the Bris
    > Sextant has to be rotated in the "pitch" direction and moved vertically
    > up or down to bring the successive sun images into the field of view.
    
    Yes, this is a problem. No telescope has the field of view wide enough
    to show all 8 Suns:-)
    
    >the binocular adapter would have to be adjustable in two directions,
    >a tricky design problem.  (It might turn out that only tilt is required
    >if only one sun image, that near the horizon, was needed.)
    
    One direction should be enough, "pitch", if the axis of rotation is chosen
    properly.
    
    > Pity the poor navigator in the past who used a cross-staff!
    
    I believe those guys were not that stupid and used a BACKstaff.
    In a backstaff you align the Sun shade with the horizon, rather
    than the Sun iteslf.
    I saw two marvelous devises
    of this sort, genuine ones, perfectly preserved since XVII century,
    in the Schiffahrtsmuseum in Bremerhaven, the best miseum of this sort
    I've seen so far. Also has two Pistor and Martins reflection circles.
    
    So I suppose a cross staff could be only used safely for star
    observations. Unless the observer wore dark eyeglasses.
    
    > I have trouble calling this test apparatus a "Bris-Sextant" .
    
    Me too:-)
    As you can see from my messages I prefer to call it
    "Bris device".
    
    Alex.
    
    P.S. I posted several new pictures on my web site
    (also made by Bill) showing the angles he measured from
    the pictures of the device. In addition I posted some
    of my observations and computation of the angles
    between the glass panes from these observations.
    
    One interesting remark. The observations fit the theory
    only VERY approximately, when you round to 1/2 degree.
    I mean the angles I obtained do not fit exactly the
    theoretically derived pattern A, B, 2A, A+B, 2B, 2A+B, A+2B, 2A+2B.
    The disagreement with this pattern is much larger than
    the errors of these observations. (The error of observations
    was controlled by Sun SD and by repeated observations, and it
    is about 2'-4'). This indicateds that the glass panes in my Bris
    are actually of very poor quality:-) I mean the surfaces of one
    pane are not parallel.
    However, this does NOT affect the preformance of the device, and this is
    the main beauty of the inventor's idea.
    
    Alex.
    
    
    

       
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