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Brad wrote, about the sextant that had been used on the Caird voyage-

| Here is an image of the sextant used by Worsley.  I did not take the
image, but found it on the internet.  I contact the individual who took it
and he confirmed that it is of the sextant that tours with the James Caird
|
| You may judge for yourself as to the correctness of the painting on the
cover of the book relative to this sextant.

I now have a copy of "Shackleton's Boat", by H M Dunnett, who founded the
James Caird Society. That provides a picture of the sextant that they claim
was used by Worsley on the voyage. Not Worsley's own sextant, however; he
stated that he borrowed Hudson's (Endurance's navigator) for the voyage,
because he found it easier to use on the boat (without saying why). The two
pictures are not identical, but it looks as though the sextant is. It all
fits.

That instrument, you can tell from the angle of the spindle for the
adjustment knob, is a Heath Hezzanith "endless tangent" model, which doesn't
use a shoe and clamp, which would call for resetting when it reached the end
of its range. It was constructed just like a micromter sextant, except that
its angle wasn't measured by turns of a calibrated drum, but by a Vernier
scale. Indeed, one turn of the drum didn't need to correspond to one degree
of observed angle; the pitch of the rack could be (and usually was) much
finer than that. It was a half-way step in the transition from Vernier to
micrometer sextant, but made no great demands for accurate machining of rack
and worm. I wonder if the endless tangent was the feature that Worsley
liked, which his own sextant didn't provide?

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.

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