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    Vernier sextant etc
    From: George Huxtable
    Date: 2006 Oct 27, 15:23 +0100

    Henry Halboth [Navlist 1480: re Cleaning arc of Vernier sextant]
    worried that his posting about using "fag ash" to clean the arc of a
    vernier sextant hadn't got through. Let me assure him that it had, and
    that its message was valued and taken to heart.
    
    The reason why there wasn't a quick response was not not due to
    discourtesy. I wanted to see what other suggestions showed up before
    replying. In the end, there was no other practical proposal except
    his.
    
    The next morning after I collected my new (old) instrument, I was off
    to Germany for a couple of days, and on returning have discovered
    Henry's follow-up messages and others in my inbox. And one of those,
    again from Henry, added this excellent advice-
    
    "If the truth were to be known, the conventional wisdom of my day was
    to
    leave the sextant alone, crud and all. The more encrusted a sailor's
    sextant might be, the more experienced he (no shes then) and competent
    he
    was thought to be. The cigarette/cigar ash polish was advanced as an
    alternative for the fastidious to use. How times have changed!"
    
    And that's the guidance I might well follow. I have no yen to display
    the thing as a shiny decoration; only to make it as readable as I can
    to my eyes, which are well past their sell-by date. I haven't had a
    real chance to play with it yet and find the best way to illuminate
    the Vernier. But at first glance, there does seem to be a bit of a
    difficulty, arising from the bevelling of the Verner scale in its
    overlap against the main arc. I can shine light on either arc or
    Vernier, and light each in such a way that the scale divisions (to 10'
    on the main arc, 10" on the Vernier) show up clearly in the
    reflection. But not both at the same time, because of the differing
    tilts of those scales, and both need to be seen clearly to align one
    arc against another. I take my hat off to the old navigators who had
    to do the job by a lantern, lit by candle or whale-oil. Some
    experimentation is called for. This may be a problem that others (such
    as Henry) are familiar with, though even in his early days, electric
    light may have been available...
    
    Not cleaning it with ash would overcome the problem of having to learn
    to smoke. In my own young days, I only ever tried smoking a cig when a
    sufficiently attractive girl would offer me one at a party. So my
    failure to pick up the habit is evidence of my lack of success in that
    direction. I don't know about Henry's habits, but I think of him as a
    consumer of the finest Havanas, hand-rolled on the thigh of a dusky
    Cuban maiden. Such is the power of imagination...
    
    If I try the fag-ash suggestion, in the end, I can always come to an
    arrangement with my local pub for the contents of their ashtrays,
    before it becomes illegal to smoke in pubs, next year.
    
    ==========================
    
    My visit to Germany may be of interest. It related to Tobias Mayer,
    the progenitor of the Moon prediction tables, on which Maskelyne's
    lunar distances were based, for the Nautical Almanacs from 1767.
    
    There's a town not far from Stuttgart called Marbach, with a little
    museum dedicated to Mayer,  in the room where he was born. And a group
    of enthusiasts who keep his memory going, because the Moon predictions
    were only a small part of his immense scientific output, though he
    died at only 39. Steven Wepster and Herbert Prinz are also members. I
    went to give them a little talk (in English, but with an on-the-spot
    translation into German), not on Mayer's mathematics, but on his
    Repeating Circle, for precise lunar-distance measurement.. Whether or
    not they enjoyed it, I can't say, but I got lots of penetrating
    questions. Joan and I enjoyed it immensely, and the German hospitality
    that went with it.
    
    George.
    
    
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