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About the method Bligh would have used, to predict the time of local noon
based on a morning Sun observation, Frank wrote-

"I suspect this trick would be most useful in near-overcast conditions.
Though you might not see the Sun enough times to convince yourself that it
has reached its peak at noon, if you can look at a local time watch
(corrected for the run of longitude from when it was set earlier in the
day) then you don't need to see the Sun for more than the ten or fifteen
seconds it takes to get a single altitude."

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Well, it was even more useful than that. As long as the time of noon had
been accurately predicted, then an observation of Sun altitude didn't need
to be taken right at noon, or even very near to it. It could be taken up to
an hour or more either side of noon, whenever a glimpse of the Sun appeared
through the clouds.  And then, the latitude could be readily calculated
from the altitude at that moment, knowing the time difference from noon,
using the Ex-meridian Tables. That was primarily what those tables were
for.

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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