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    Re: Problem with a sextant
    From: Alexandre Eremenko
    Date: 2006 Apr 26, 09:17 -0400

    Dear Joel,
    I looked at the web and now I have an impression
    of what a dial inficator is:-)
    Could you explain more, how exactly you propose to
    apply it to the problem? You suggest somehow to measure
    the uniformity of the teeth?
    (I am really interested, but I am almost completely ignorant
    in precision mechanics).
    On Wed, 26 Apr 2006, Joel Jacobs wrote:
    > If you want to trace out the problem,
    > you can buy a dial indicator for not much money.
    > Maybe $25.00 at Lowe's or Home Depot. It would have other uses.
    > In other messages you mention the writings of others
    > who experienced an unexpalined change in their instruments over time.
    > just wonder if some of that might not be due to changes in climate as
    > they move from one location to the other. The early instruments were
    > made
    > primarily of ebony and ivory and I would think their expansion and
    > contraction could be a function of temeperature and humidity.
    The instruments are precisely described by the author.
    These were 15 inch bronze sextants made by the best instrument
    makers of that time (Ramsden, Dollond and Bird). At least one of these
    instruments survived and I have its picture.
    To my understanding, they should not be more vulnerable to temperature
    changes than modern sextants. (Bird, Dollond and Ramsden were perfectly
    familiar with the problem of temperature expansion and took care of
    it as one can see from their own writings). Humidity should be irrelevant,
    of course for metal sextants.

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