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I doubt if Frank Reed and I are going to agree much about whether Slocum
took just one lunar on his circumnavigation, or whether he made it a common
practice. Perhaps it may have been something between the two.

Frank argues that Slocum's position, South of Rio, that was agreed with a
ship was by dead-reckoning over the few days since leaving Rio, and not by
lunar. I agree that it's a plausible explanation, and doesn't prove (or
disprove) that a lunar was taken at that time.

Frank appears to accept the lunar longitude between Juan Fernandez and
Nukuhiva.

I quoted the account, a few days out in the Arafura Sea, in which Slocum
says, after mentioning some noon Sun latitudes-

"But the greatest science was in reckoning the longitude. My tin clock and
only timepiece had by this time lost its minute-hand, but after I boiled
her she told the hours, and that was near enough on a long stretch."

Frank dismisses this-

"He's talking about dead reckoning. If you want to know how far you've
travelled in four hours, you need to know what four hours is. The minute
doesn't matter much when you're doing five knots."

I really don't see how Frank infers that Slocum's statement relates to dead
reckoning..

1. Slocum used the word "reckoning" for both dead-reckoning and for lunar
longitude, as in his account in the Pacific, off Nukuhiva, when he says
"The verified longitude when abreast was somewhere between the two
reck=onings".

2. He towed a rotating log, which would indeed give him information about
longitude; particularly on a mainly West-going passage, as this was. But
for that, there was no input AT ALL required from a clock. It wasn't a
speed-log, it was a distance-log. So why would Slocum refer to his clock,
if that log was where his longitude was derived from?

3. I'm sure Frank and I would agree that that tin clock wasn't being used
for any form of "longitude by chronometer".

4. If it was just a matter of dead-reckoning from a log, why would Slocum
refer to it as "the greatest science"?

===========

We have to remember that Slocum was writing a journal for the ordinary
reader, not a log for the interest of Nav-l listmembers. Having described
taking lunars once, in the Pacific, we shouldn't expect him to refer to
each lunar observation thereafter in his text. He must have taken hundreds
of noon latitudes in the voyage, but only occasionally did he refer to
doing so in his account. It is indeed a pity that his log no longer exists.
Slocum devoted more space to the places he arrived at, than to the passages
between.

So we can't infer, from a shortage of references to lunars, that (except
for that once) he didn't take them. Nor, I accept, can we infer that he was
taking them all the time. The truth may lie somewhere in-between. But it's
a clear claim by Frank that I argue with, a claim that Slocum used lunar
distances only once, in the Pacific. Sparsity of evidence for is not the
same as evidence against.

We know, from his son Victor's account, that he made a practice of checking
his chronometers against lunars, during his long career as master of a
merchant vessel, perhaps one of the last ship's captains to do so. So he
was very familiar with the required skills, though may have got a bit
rusty.

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

Sorry to have misplaced a comment made by Slocum, from his Pacific passage
where he made it, to the Indian Ocean (as Frank pointed out).

Frank added->And you wrote:
>"In the hands of skilful observers and patient computers the Lunar Method is
>reliable within a quarter of a degree longitude, which would be the distance
>of a high landfall..."

That was me quoting the words of Slocum's Son Victor, not my own words. I
wouldn't really disagree, though for observations at sea I suspect it was a
bit optimistic.

George

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contact George Huxtable by email at george@huxtable.u-net.com, by phone at
01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
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