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Frank wrote, about the source of old ships logs and journals recently made
available in the CORRAL website-

"Hey, that's wornderful! Finally some primary source data from 19th century
British vessels. "

Much data has been available, via various libraries or the National Archive
at Kew, but not online. I have recently investigated such data from early
Cook logs and from Arctic whaling voyages, but none of these are in the
CORRAL database. This is the first time, that I know of, that such a
collection of digitised data has become available online. I hope there will
be more..
He asked- " Have you discovered any interesting navigational data in these
logbooks yet?"

No; as soon as I saw what was available, I thought to share the information
with Navlist. Nor will I be able to do much investigation within it just
now; it will have to wait a while. It's there for anyone that would like to
burrow in.

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

In the meantime, let me share something that has been puzzling me a bit,
about observations from another Cook voyage.

We noted, a while back, that the astronomical observations from Cook's
third voyage (Bayly, Cook, and King) had been kindly made available on-line
by the Canadians at-
http://www.canadiana.org/view/17414/0003
And if you go to page 43, that's a page showing lunar distance observations
taken at Ulietea, in 1777. I took a look at this page in the hope that it
would throw a bit of light on the observations taken at the same spot in
the second voyage in 1773, because we had only a single page of transcript
from that second voyage. It didn't throw much light, in the end.

Note how the Sun column is shown as an altitude, but for some reason the
Moon is shown as a ZD; presumably Zenith Distance. Why should this be?
Well, it strikes me that this may be a use of the sextant fitted with
backsight. If the Moon can only be seen over the island, so would call for
an estimation of dip-short, can it be that instead, the Moon altitude is
being measured up from the opposite horizon? Does that explain the use of
ZD? Can anyone suggest another reason for logging ZD for one body, and
altitude for another?

Now to the bit that's been puzzling me. It relates entirely to the first
four observations, on 7 Nov (nautical date). A set of lunars was taken by
Cook and King simultaneously with different instruments, then another set,
with the instruments swapped over, a few minutes later; a good, scientific,
procedure. But the observations are very discordant, by over 4 arc-min,
even though the index errors differ by only 35". And it's the two observers
that are 4' apart, not the two sextants. And in the time interval, of over
4 minutes, there's been no change in lunar distance. And the differences in
deduced longitude don't reflect the differences in lunar distance. What's
going on? It looks as if there were serious transcription errors. In which
case, we have to be careful about accepting such tables of numbers at face
value. Am I missing something?

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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