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    Re: Re Re: Dream Choice of Sextant
    From: Alexandre Eremenko
    Date: 2005 Aug 12, 17:06 -0500

    I don't understand this business of "titanium dream":
    Modern metal sextants are made either of a copper alloy
    or an aluminium alloy. Both types of alloy seem absolutely perfect
    for a sextant frame: high rigidity, high heat conductivity, and
    corrosion sesistance.
    Aluminium has an advantage of being much lighter.
    
    What advantages do you expect from a stainless steel,
    silver or titanium frame?
    
    (Silver and platinum were used in sextants which had no drum,
    where the angle was read on the main arc directly through
    a microscope. But this is a completely different matter).
    
    Let me explain one important advantage of this old arrangement.
    The modern sextant has TWO places where high precision workmanship,
    dust and dirt, and also wear can be essential:
    the axis of the arm and
    the teeth-wormscrew assembly.
    The older sextants have only one such sensitive place: the axis.
    There is no backlash, no wear of the wormscrew, no dirt,
    no sea salt or insects between the tooth and the wormscrew.
    Just because there is no wormscrew and no teeth.
    
    The only disadvantage is a bit slower reading, and usually
    they came without illumination. On the other hand, they typically come
    with 3 scopes of highest quality, extra eyepieces and an eyepiece filter.
    
    I tried some of those fine old instruments in antique shops in
    Germany and France, and was very impressed. Unfortunately,
    each of them in good condition usually costs more than
    the most expensive new sextant.
    
    Alex.
    
    P.S. Even more interesting things I've seen in the European museums.
    (Including 2 Pistor and Martin reflecting circles
    (Chauvenet says that these are the finest ones), and even a genuine
    XVII century backstaff (in Bremerhaven), in perfect condition, like new:-)
    Unfortunately, they won't let you try any of these instruments,
    and I even did not carry a camera with me. But I made sketches.
    A
    
    
    
    On Fri, 12 Aug 2005, Bruce Stark wrote:
    
    > Someone else will have to throw cold water on Robert's titanium sextant
    > dream. Never had anything to do with titanium myself.
    >
    > I've had a special respect for Eno since the1990's, when we first
    > corresponded. He was so keen he was taking his sextant and artificial horizon out in the
    > sub-arctic winter nights to get observations. He must be a savvy outdoorsman,
    > because he did it all without losing a single finger to the cold. Also, Robert
    > was among the first to use my "Tables for Clearing the Lunar Distance," and
    > wrote a helpful "Field Assessment" of them for the "Navigator's Newsletter."
    >
    > Bruce
    >
    
    
    

       
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