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    Re: Electrical Wire (minus 30???)
    From: Robert Eno
    Date: 2004 Mar 24, 17:59 -0500

    Trust me. I am sure about the temperatures. Dress for it and it isn't all
    that bad.
    
    Keep in mind that Robert Peary and Roald Amundsen used sextants for
    navigating to the North and South Poles and under the most horrendous of
    conditions. Add to that, they probably used those awful vernier sextants
    which are difficult to read under the best of conditions. I'm lucky. All I
    have to do is take my sights and scurry back into the house to reduce my
    sights with a scientific calculator and a hot cup of tea (or rum, depending
    upon the time of day) to lubricate the process.
    
    As for sextant calibrations, it is necessary to leave the sextant outdoors
    for at least 15 - 20 minutes in order to bring it to the same ambient
    outdoor temperature. Check for side error and index error as usual. I have
    never had any problems with regard to the perpendicularity of the index
    mirror with the body of the sextant.
    
    At low temperatures and especially for bodies with altitudes of less than 30
    degrees, it is a good idea to use Table 23 (temperature correction) from
    Bowditch.   I don't usually bother with table 24 unless the barometric
    pressure is unusually high or low.
    
    What drives me to do this???  Do you really need to ask this question on a
    forum which is comprised of die-hard luminaries who spend their spare time
    studying some of the most oddball topics like the nuances parallax and lunar
    distances and the exact astronomical time of equinox???? I do what I do for
    the same reason as everyone else on this list: a sheer love and devotion to
    astro-navigation and a desire to perfect our sacred and dying craft. Believe
    me, I much prefer to take a round of sights on a warm summer day with the
    sun shining and the birds a twittering! But alas, it is winter and such
    dreams are not to be.
    
    Thanks for the tip on the wire by the way.
    
    Cheers,
    
    Robert
    
    
    
    ----- Original Message -----
    From: "Keith Williams" 
    To: 
    Sent: Wednesday, March 24, 2004 10:58 AM
    Subject: Re: Electrical Wire (minus 30???)
    
    
    > Are you sure you are using (or intending to use) a
    > sextant at minus 30 or minus 40 (the latter being the
    > same in degrees F and degrees C)?
    >
    > Without really good head protection (which would make
    > using a sextant very difficult), my head hurt at that
    > kind of temperature sufficiently to stop me being able
    > to concentrate enough on any task as demanding as
    > taking a sight...let alone the risk to skin from
    > touching bare metal (and probably even from eyecup
    > rubber, too) ..
    >
    > Are sextant calibrations valid at those levels?
    >
    > But as I've lived in temperate and hot climates, with
    > only limited exposure to such extreme cold, I'm not as
    > tough as I should be.
    >
    > Please tell us what drives you to do this!!
    > best regards, Keith Williams
    >
    > PS - tinned wire doesn't "corrode" as quickly as
    > untinned, which has a life of maybe 10 years in
    > temperate salt-laden-air conditions (verigris builds up
    > and the wire loses its coppery-nature even inside
    > insulation and esp at connections, so resistance builds
    > up, which can stop yopur equipment or even create a
    > fire). But at minus 30 or so, I bet corrosion is a
    > totally different game
    >
    >
    
    
    

       
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