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    Re: Old Sextant on German money
    From: Alexandre Eremenko
    Date: 2007 Mar 9, 14:50 -0500

    Dear George,
    Now I reply your message:
    > List member Peter Ifland, in his book "Taking the Stars",
    > got there before Alex did.
    > His figure 45
    George, I have this book, and certainly I checked
    all available pictures of sextants of this type before
    I posted my message. Not only in the book but also on the
    Internet. I also studied the bank note with the strong
    magnifying glass:-) It is pretty clear.
    I am mostly concerned with the Index mirror.
    > That double-mirror makes no more sense to me than
    > it does to Alex. I wonder whether the engraver was
    > working from a real
    > sextant, as Alex assumes, or was doing his best to
    > interpret another
    > drawing.
    In other words, you conjecture that this double mirror is
    the artist's phantasy. This idea did not occur to me:-)
    > The engraver was unlikely to understand the
    > workings of what he was drawing.
    Probably. But I thought that for such a serious task as a picture
    on the money they would use a real sextant in front of the artist,
    and the picture will be also approved by the experts before going
    to print:-) Notice that other pictures on this note are
    remarkably accurate: the triangulation net, the "bell curve"
    and even the formula that describes this curve!
    I do not assume that the engraver understood what he was drawing,
    but I assume that those who designed the note consulted
    historians and mathematicians.
    > Alex refers to the large disc which moves with the magnifier,
    > clearly
    > shown in figure 45 and also in one of the sextants of figure 49.
    > Its purpose puzzles me too.
    > My speculation is that it might be backed with
    > a white disc on the unseen side, which would reflect diffuse light
    > to the Vernier from an oil-lamp or candle placed close behind the
    > sextant, at the same time shielding the observer's eye from that
    > direct light. Just a guess.
    I like this guess very much.
    Very early I discovered that reading my vernier sextant
    scale at night is almost impossible. (It gives me hard time
    in day light as well:-)
    I am using a very small light diode flashlight which I try
    to direct at the diffusor. It does not work well.
    It shines to my eye instead of illuminating the scale.
    Any suggestions?
    How was it really done in the old times?
    I mean the vernier without the disc we discussed above,
    just the ordinary construction with a diffusor above the
    vernier, or without a diffusor.
    How exactly did they illuminate the scale?
    With some specially designed oil lantern which sends the
    light down?
    > Another puzzling matter, to me, is the relevance of a hand-held
    > sextant to a survey triangulation on land.
    I recently read a biography of Gauss. It is mentioned there
    that he was a big fun of sextants:-) He would just go around
    and measure all sorts of terrestrial and celestial angles
    for pleasure. (Just as I do:-)
    Of course the triangulation which is shown on
    this bank note was not done with sextants. But the book mentions
    that Gauss nevertheless would always curry his sextant around
    during the triangulation. It also mentions that it was a Troughton
    and Simms, but he had several other sextants.
    I wonder whether this particular Troughton and Simms which
    belonged to Gauss still exists.
    There is no Gauss museum in Gottingen, (let me say more precisely:
    I did not find any:-)
    and the observatory where he worked seems completely neglected.
    Another question touched in many books is why Gauss did this
    triangulation at all:-) At that time he was in zenith of his glory,
    everybody was calling him "The Emperor of Mathematicians",
    and certainly he could spend his time doing something no one
    else except himself could do, instead of doing this routine job.
    Nevertheless, he spent more than a decade (!) doing this survey.
    But this is a topic out of scope of this list.
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