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    Re: Advice concerning sextants
    From: George Huxtable
    Date: 2010 Feb 23, 19:42 -0000

    Ken Gebhart wrote-
    
    "...2.  Whole horizon mirrors do not divide the light.  They have a
    specialized coating which transmits a large percentage of light, while at
    the same time reflects a large percentage of light.
    
    I don't fully understand what Ken's saying here, but whatever it is, I'm
    inclined to disagree.
    
    Such a mirror can reflect some light, transmit some light, and absorb some
    light. The total has to add up to 100% of the incident light. It can't
    create light that wasn't there. So it DOES divide the light, as best it can,
    between reflecting and transmitting, absorbing as little as possible. What
    else is Ken telling us?
    
    The most pithy description of whole-horizon mirrors is that they make easy
    sights easier, and difficult sights harder. But I've had very little
    personal experience with such mirrors, so am not competent to express an
    opinion.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "Ken Gebhart" 
    To: 
    Sent: Tuesday, February 23, 2010 5:15 PM
    Subject: [NavList] Re: Advice concerning sextants
    
    
    |I would like to make two comments about Jim's posts:
    | 1.  Bigger mirrors do not give more light. (Is your image while
    | shaving with a large bathroom mirror brighter than with a small one?)
    | 2.  Whole horizon mirrors do not divide the light.  They have a
    | specialized coating which transmits a large percentage of light,
    | while at the same time reflects a large percentage of light.
    |
    | Ken
    | On Feb 22, 2010, at 11:40 PM, James N Wilson wrote:
    |
    | > John reminds me of my first experience with the whole horizon sextant
    | > mirror, which I called the half silvered mirror, was that finding the
    | > horizon in dim light was difficult. I found no advantages, in that the
    | > sun and moon images can be seen in the clear part of the mirror,
    | > aiding
    | > in bringing them down.
    | >
    | > Now, if someone would make a horizon mirror that was half silvered on
    | > only the left side, that might be worth something. But I might
    | > still have
    | > the same problem at twilight, where I need all the light available
    | > to see
    | > the horizon.
    | >
    | > I'm sure that the article mentioned noted that half silvered
    | > mirrors (one
    | > way glass) allow only a portion of the light to pass. When we
    | > remodeled
    | > our bath, we had one installed in our shower for privacy. The room was
    | > significantly darkened, and plants wouldn't grow. The amount of light
    | > reduction is significant.
    | >
    | > Jim Wilson
    | > ____________________________________________________________
    | > Nutrition
    | > Improve your career health. Click now to study nutrition!
     
    | > cp=NVIXY2oLGPGa1TCho6UV4QAAJ1D3lHlZVltl3Pnu3pZYfILRAAYAAAAAAAAAAAAAAAA
    | > AAADNAAAAAAAAAAAAAAAAAAASQwAAAAA=
    | >
    | >
    |
    |
    |
    |
    
    
    
    
    

       
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