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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?

George.

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" 
To: 
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 
and
by a Husun “three ring” micrometer sextant over the counter most anytime 
after
1943, or thereabouts – IMHO this latter simple sextant contributed 
materially
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 
personally
have never seen such an instrument without this drive arrangement, which was
also incorporated into the vernier type sextant by Plath in later years, 
thus
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 
clamp
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 
“salty
old dog”. Well sir, this old dog navigated me over a good part of the world 
and
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 
catch
the AM train to Glasgow, where the Winfred O. White establishment was 
located
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 
owned
and used German, Japanese, and British micrometer sextants of every
description, but finally settled on a relatively simple Plath, certificated 
in
1946, fitted with a 10 second double spaced vernier, and endless tangent 
screw,
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.



Regards,



Henry







--- On Fri, 1/8/10, FrankReed@HistoricalAtlas.com 
 wrote:

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 
kidding).-FER
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