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    Re: Making an artificial horizon -- seeking a source for optical flats
    From: Geoffrey Kolbe
    Date: 2011 Jan 23, 06:16 +0000

    >Incidentally, my plan was to make a setup 
    >similar to the breathtakingly expensive 
    >Freiberger artificial horizon available from various sellers.
    I looked up the price being asked by various 
    sellers - around �500... Ouch! I bought mine many 
    years ago when the price was nowhere near so horrifying.
    Many years ago I played with the idea of floating 
    a glass mirror on a bowl of mercury. The 
    advantage of using mercury was that surface 
    tension effects kept the glass "raft" from 
    touching the sides of the bowl. This is a problem 
    that is going to afflict anyone who tries 
    floating the raft on water - the raft will head 
    straight for the side of the bowl (or seem to) and stick there.
    There were, however, problems in trying to float 
    a glass mirror on mercury. The mirror would not 
    sit flat. On floating a piece of clear glass, the 
    problem became apparent. Due to the fact that the 
    surface of the mercury was not scrupulously 
    clean, irregular bubbles of air were being trapped under the glass.
    I decided that these problems were too much to 
    cope with and that these were obviously the 
    reasons why this form of AH had not gained any momentum before.
    Geoffrey Kolbe

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