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    Re: Sextant frames
    From: Bill Morris
    Date: 2009 Apr 16, 13:53 -0700

    Brad and Jeremy
    The coefficients of linear thermal expansion of bronze and Dural are very 
    similar at 18 and 23 x 10^6/K respectively. However, their thermal 
    conductivities are not. The figures given for bronzes are 42 - 50 W/(mK) 
    while for Dural it is 164 W/(mK). In other words, aluminium alloy conducts 
    heat much better than bronze and will equilibrate with its surroundings 
    quicker. An alloy sextant left in the sun will get hotter all over quicker, 
    but will also cool quicker. 
    The T in SNO-T means that the sextant  is Tropicalised and presumably the 
    paint has high reflectivity. I will leave it in the sun with a black-framed 
    instrument, compare temperature rise with  thermo-couples front and back and 
    report back.
    Bill Morris
    Navigation List archive: www.fer3.com/arc
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