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    Sextant development:was Re: Sextants in Little Rock
    From: George Huxtable
    Date: 2010 Jan 9, 10:35 -0000

    Henry (hch) raises several interesting points about sextant development.
    I wasn't aware that during the earlier years of World War 2, drum  sextants 
    were so hard to get, outside the military, in the US. How long before that 
    did drum sextant manufature in the US start, then, and by which firm(s)?
    We can imagine why supplies were so short. Each new vessel would be 
    replacing another that had been sunk by a U-boat, and gone down, most 
    likely, with its navigators and their sextants.
    When he bought his Husun sextant in Glasgow during the war, was that a new 
    instrument? I wonder if the sale of such sextants was then restricted, and 
    whether Henry had to show any documents to buy it? Perhaps, in those days, 
    his American accent was enough... It would be quite a feat of memory to 
    recall such details, from 60-odd years back; unfair to ask, perhaps.
    And it's interesting to learn that after experience with both Vernier and 
    drum instruments, Henry settled on a Vernier Plath, because of its superior 
    optics. That, it seems, was more important to him than the easier-reading of 
    the modern drum. The main trouble with a Vernier instrument, it seems to me 
    (after very limited practical experience), is the difficulty in getting 
    precise readings from the Vernier scale for twilight observations, 
    particularly in poor lighting. Would there always be electric lighting 
    available on the bridge in Henry's early days, or were some oil lamps still 
    in use? I can remember a passage on a steam coaster, from Liverpool to 
    Belgium, around 1950, in which all lighting was still by oil lamps. I am 
    aware that bright lighting is to be avoided, to preserve night vision, but I 
    wouldn't relish reading a Vernier under oil-light, even in the days when my 
    eyes were much sharper than they are now.
    I remain puzzled by one aspect of the transition from Vernier to drum 
    sextants. The first Plath drum instruments were in their catalogue from 
    1907. However, they didn't appear in the catalogues of Heath, or Hughes, 
    until the late 1920s. Even if the Germans were ahead with their machine 
    tools, I find it hard to explain the 20-year gap.Even if Plath had the 
    patents sewn up, patents don't last that long, and German patent rights were 
    unlikely to be given much respect during a World War. Were the new-fangled, 
    foreign, drum instruments distrusted by non-German mariners? Was there any 
    basis for such distrust? Were they eagerly accepted by German navigators? 
    Did those early Plath drum instruments achieve the same precision as their 
    Vernier counterparts? I wonder if opinions, around that time of the 1910s, 
    can be found in pages of the nautical journals.
    Once Heath had introduced the "endless tangent screw" to their Vernier 
    sextants, it might be imagined that they were most of way towards the drum 
    sextant. All they had to do next, it seems, was to replace the simple knob 
    by a graduated drum, and make the screw-pitch correspond to exactly 1 degree 
    on the scale. That last requirement , however, called for extreme precision 
    of both rack and worm. Was Heath's technology simply not up to the job?
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message ----- 
    From: "hch" 
    Sent: Saturday, January 09, 2010 3:26 AM
    Subject: [NavList] Re: Sextants in Little Rock
    Hi Frank,
    I believe it safe to say that by the mid-1940s transition
    from vernier to micrometer drum sextants was well underway, if not actually
    completed. It as just that the micrometer drum sextants were not generally
    commercially available in the USA – certainly the military, both Allied and
    Axis, had them and they were being issued to new built merchant ships by the
    Maritime Administration, but over the counter sales were non-existent or, at
    least, very limited, thereby extending the life and availability of older
    vernier sextants which could still be found on the 2nd hand market
    The opposite situation prevailed in Great Britain where you could walk in 
    by a Husun “three ring” micrometer sextant over the counter most anytime 
    1943, or thereabouts – IMHO this latter simple sextant contributed 
    to the winning of the Battle of The Atlantic, and most Allied Seamen that I
    knew aspired to owning one.
    Micrometer sextants apparently were around, although not
    plentiful, since at least the 1920s, facilitated by the incorporation of the
    rack and pinion drive arrangement for movement of the index arm – I 
    have never seen such an instrument without this drive arrangement, which was
    also incorporated into the vernier type sextant by Plath in later years, 
    doing away entirely with the old style index arm clamp and friction fine
    adjustment arrangement in which the tangent screw could come “two blocks”.
    My first “sextant” was actually a John Bliss & Co.
    octant, purchased second hand (more likely third to fifth hand) at their
    establishment on Pearl Street in New York City in late 1943 – it was then
    probably in the order of 60 to 80 years old, had the old style index arm 
    and limited run friction fine adjustment device for a 15 second vernier, and
    was encrusted with a dark green coating of verdigris, making it a real 
    old dog”. Well sir, this old dog navigated me over a good part of the world 
    competed favorably in every day sights, including stars, with any modern
    sextant it came up against; it stared my lifelong affinity fort vernier
    sextants – I still have it today.
    Subsequently, I did join the crowd. While lying on the hook
    in the convoy anchorage off Gourock, Scotland, I got enough time off to 
    the AM train to Glasgow, where the Winfred O. White establishment was 
    directly across from the Station, purchase a Husun “three ring” sextant for
    about $60.00, and return to my ship by way of the PM train. I have since 
    and used German, Japanese, and British micrometer sextants of every
    description, but finally settled on a relatively simple Plath, certificated 
    1946, fitted with a 10 second double spaced vernier, and endless tangent 
    i.e., rack and pinion drive. My preference for the Plath resides primarily 
    in the
    telescope, which I simply find to be personally more comfortable in use.
    Sorry to offend those who don’t like sea stories, but you
    did ask.
    --- On Fri, 1/8/10, FrankReed@HistoricalAtlas.com 
    From: FrankReed@HistoricalAtlas.com 
    Subject: [NavList] Re: Sextants in Little Rock
    To: NavList@fer3.com
    Date: Friday, January 8, 2010, 11:27 AM
    Henry, you wrote:
    "The term "endless tangent screw sextant" was a common expression for the 
    sextant sub-type possessing such a device, prior to the common usage of the 
    endless or geared tangent screw - it it recognized as a sextant sub-type by 
    definition in HO 220."So then, circa 1940-45, it still would have been "new 
    enough" that a sextant would specifically have been referred to as "endless 
    tangent screw" as a novelty? Was your first sextant a micrometer sextant? 
    And was this distinct from an "endless tangent screw" sextant? Or were all 
    micrometer sextants also "endless tangent screw" sextants?You added:
    "The abbreviation ETS is not, however, a recognized or, at least, defined 
    abbreviation except in the imagination of the originator. Today, folks seem 
    to make up abbreviations as they go along and everybody else is expected to 
    understand - apparently a requirement of the electronic age. "This bugs the 
    hell out of me, too. It's the era of acronyms. Linguists say it started 
    around 1925. Before then, you will almost never find acronyms (famously, 
    this is one of the reasons why you can be sure that "POSH" was not an 
    abbreviation for "port out, starboard home" as in the popular 'folk 
    etymology'). Acronyms are now everywhere. But it's not going to change, so I 
    guess we better "learn to love and live with acronyms" -- a policy which I 
    call "LLLWA" or in print "L3WA" (so there's no misunderstanding... I am 
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