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    Re: First sights
    From: Robert Eno
    Date: 2007 Jan 22, 08:37 -0500

    I would avoid mercury like the plague. It is very dangerous stuff -- even if
    you can get it -- as it volatilizes at room temperature. Mercury vapours are
    not something you want to inhale, even in small amounts. I suggest a pan of
    waste oil. Something black and somewhat viscous. Only drawback: you get a
    lot of detritus on the fluid and it is nearly impossible to clean. Down the
    road, I would invest in a glass artificial horizon. I have been using one
    for years and I love it. Only drawback: it must be perfectly level.
    
    I had a few experiences similar to Gary. Once from my boat last summer and
    once from the shore of beautiful Hall Beach. In the former case, I took a
    round of sights off the water, and then switch to my bubble attachment.
    Unfortunately, I cannot boast about the results. Still, it was fun.
    
    Robert
    
    ----- Original Message -----
    From: "GAry LaPook" 
    To: 
    Sent: Monday, January 22, 2007 6:38 PM
    Subject: [NavList 2125] Re: First sights
    
    
    >
    > Gary LaPook wrote:
    >
    > You can also take sights using an artificial horizon.
    > To make one of these simply put water in a saucer (or,
    > much better if you can get it, use murcury) and the
    > surface of the liquid will be perfectly horizontal.
    > Measure the altitude of the star using its reflection
    > in the saucer as the reference point instead of the
    > horizon. Due to the geometry of the situation (angle
    > of incidence equals angle of reflection) you end up
    > measuring exactly twice the altitude. Then simply
    > apply the index correction and divide the remainder by
    > 2, then apply refraction but not dip corrections. You
    > need a still night so that the wind doesn't ripple the
    > surface of the water. I have been using a small bottle
    > of murcury for over forty years for this and because
    > of its reflective quality I can take second magnitude
    > stars such as polaris, with water you can shoot first
    > magnitude stars easily. If shooting the sun make sure
    > you use both sets of shades and line up the lower limb
    > with its reflection in the liquid which will be the
    > top of the sun's reflection.
    >
    > I remember one night in 1990 we were anchored in a
    > long fjord on the east coast of Tahaa (an island about
    > 20 nm east of Bora Bora) and it was so still that I
    > could see the stars reflected in the ocean around the
    > boat. I got out my Tamaya and took a round of sight
    > and got a fix that crossed on our anchorage.
    >
    
    
    
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