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Brad wrote-

"It is important to differentiate between various portions of the
expedition.
1) Boat navigation from New Zealand through the South Ocean and into the
Pack Ice.
2) Trapped in the Pack Ice.
3) The phenomenal 800 mile journey in the James Caird."

I would divide it further. During the period between Endurance being trapped
and when she sank, they had access to all their chartroom gear, and could
navigate just as when she was under way, using chartroom and chart-table.

They had to leave much equipment behind after taking to the ice dragging
boats.

Then when they got out of the ice, there was real boat-navigation again, to
reach Elephant Island.


"I have not investigated (1), although Shackleton gives precise Lat Long
coordinates.  I would be very surprised if Worsley used an alternate method
here.  That is, I think he used noon latitude and AM/PM longitude."

On ship, positions might have been obtained by crossing a morning position
line, drawn on a chart at right angles to the Sun's calculated azimuth, with
a noon latitude line. Or they might have been obtained by trig calculation
of longitude, knowing noon latitude, as was done in pre-Sumner days. Unless
the working was shown, it might not be easy, just from the resulting
position, for us to decide on which method was in use.

But once the vessel had sunk, and chartroom and chart-table had gone, then
chart-based plotting methods would have become far more difficult.

"When trapped in the pack ice, Shackleton indicates that the team used a
theodolite and his sextant (probably with an artificial horizon) to "equal
effect", down to a temperature which he specifies but escapes my memory. "

I wonder how near to the freezing point of Mercury his local temperatures
got, and if he somehow needed to keep it warmed.

"When on the journey, Worsley used a Heath Hezzanith Sextant.  This sextant
tours with the Caird.  The sextant has multiple features.  It has multiple
scopes and an attachable binocular (!). Many of the scopes have the lines as
indicated by Bowditch to be used to adjust the parallelism of the scope to
the arc.  Further, there is a star scope and many eye piece filters.  Quite
the advanced sextant, with so many options."

We have to tread rather carefully here. Was Worsley, in those words,
describing his own sextant? Because on the boat journey, he wrote about the
sextant that was taken- "This sextant, one of Heath's, had been presented to
Hudson, Navigating Officer of the Endurance. I found it more convenient for
use in the boat than my own".

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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