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This is a follow-up to my posting yesterday, trying to follow the details of 
a page in Worsley's log, from the James Caird's voyage to South Georgia. 
It's mainly for Brad, and for anyone else who may take an interest. Brad's 
transcript of that page is attached (again). Also, the corresponding page 
from Worsley's account, in his "Shackleton's boat journey". There seems to 
be a discrepancy between them, which I can't understand.

The written account clearly says that a (poor) observation was made at 9.45 
am, and then again at noon. The 9.45 must refer to local time, because at 
9.45 am GMT, it was still dark. So he is talking about an initial 
observation, a couple of hours or so before noon, which is certainly getting 
a bit close to noon for a good time-sight; presumably why he refers to the 
"lateness of the hour" as a shortcoming. There's no mention of any other 
observation, later that day

However, the left column, of Brad's transcribed log, must surely be 
representing times. And a Greenwich time of 5.10.14 , if it represents 
chronometer time of 5hrs 10 min 14 sec, will be well AFTER local noon, which 
must be at about 2 hrs 40 min or so after Greenwich noon. So it's therefore 
an afternoon observation, not a morning one. Which presumably explains the 
"P.M.", written on the same line.

That has no effect on the spherical trig calculation of local hour angle at 
the time of the observation, which ended up with 2hrs 50 min 03 sec, which 
is symmetrical about local noon, and would apply exactly the same pm as am, 
except that the hour-angle would be offset in the opposite direction. All 
this makes the time calculation, and the resulting longitude, a lot more 
understandable.

An afternoon observation, made over 5 hours after Greenwich noon, also fits 
in better with the values that Worsley used for Sun declination and for 
Equation of time, which were roughly halfway between the predictions for 
Greenwich noon on 7 May and for the following midnight, based on the 
informatuion Frank Reed provided.

========================

Yesterday, trying to understand the final adjustment that had been made to 
longitude, in the left-hand column, of 25', I wrote- "The revised value, 
marked "39º 34' Noon", can't reflect ground gained in the period up to noon, 
because it shows a 25-minute increase in Westerly longitude, and the Caird 
was travelling largely Eastward." That assumed that the time-sight had been 
made in the morning.

However, if the longitude observation had been made after noon, not before 
(as now seems likely), and Worsley wanted to back-track it to estimate the 
position they had been in at their local noon, then as they were travelling 
Eastwards, that would require shifting their position further West, just as 
he actually did. Such a 25' change would presume a speed of Easting of 5 
knots, which does seem rather much for such an under-canvassed craft as 
Caird.

========================

But if this reassessment, that it was an afternoon time-sight, is correct, 
why on Earth did Worsley write that it was at 9.45 am?  Was he, I wonder, 
writing from memory, and separated from his log-book? It's very strange. Any 
ideas?

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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