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    Re: Advice concerning sextants
    From: Ken Gebhart
    Date: 2010 Feb 23, 16:03 -0600

    George,
    I do not agree that the total must equal 100%.  Neglecting
    absorption, I agree that light going through the mirror in one
    direction would have reflection and transmission adding up to 100%.
    But where light goes through in both directions, with the proper
    coating on the glass, the sum could be greater than 100%.  I believe
    that was the whole idea of the invention of whole horizon type
    mirrors (Allview, Transflex, etc.) Am I wrong?
    
    Does anyone else care to jump in on this?
    
    Ken
    On Feb 23, 2010, at 1:42 PM, George Huxtable wrote:
    
    > 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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