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    Re: Sextant frames
    From: James N Wilson
    Date: 2009 May 22, 20:15 -0700

    A bit far fetched from the effects of thermal expansion on sextant
    frames, but some years ago I took a look at the reality of the phrase,
    "Freeze the balls off a brass monkey." Historically, the brass monkey was
    what supported the local store of cannonballs. I think that the assertion
    was that in extreme cold, the cannonballs would shrink enough to fall off
    the supporting monkey.
    Here's what I found:
    The difference in the coefficient of thermal expansion between brass and
    iron is 6x10-6. Applying that to a 4 inch diameter cannonball (and a
    similar sized hole in the monkey) times a 100 degree F temperature change
    equals .0024" on the back of my envelope. I can't imagine that such a
    minuscule change would affect the static stability of a cannonball on the
    Sorry to throw cold water on a colorful phrase.
    Jim Wilson
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