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    Re: Problem with a sextant
    From: Robert Gainer
    Date: 2006 Apr 26, 15:55 -0400

    What are you measuring with this Joel? If you mount it on the index arm how 
    does that measure the distance between teeth on the limb? Or is it your 
    intention to measure something else? Do you want to measure the change in the 
    distance from the pivot to the edge of the arc with this setup? Or are you 
    measuring how flat the frame is?
    Robert Gainer
    > From: Joel Jacobs 
    > Date: 2006/04/26 Wed PM 03:34:43 EDT
    > Subject: Re: Problem with a sextant
    > Alex,
    > I am leaving for an extended trip early tomorrow AM,
    > The trick would be how to mount it on the index arm in a fashion that would 
    allow it to measure the change in the surface of the arc. The gauge is 
    simple. It has an arm that is spring loaded and senses changes on a surface. 
    It reads out on an anolog dial which is calibrated in very small divisions.  
    There will be enough info in the booklet, but mounting it may be difficult. 
    Maybe someone in your university's engineering department can help you 
    install it on your sextant, and show you how it operates.
    > Regards,
    > Joel
    > --
    > Visit our website
    > http://www.landandseacollection.com
    > -------------- Original message from Alexandre E Eremenko : --------------
    > > 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).
    > >
    > > Alex
    > >
    > > 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.
    > >
    > > Alex.

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