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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!
 
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> | >
> |
> |
> |
> |
>
>
>

   

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