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I has three objections to Frank's conclusions:

The explanation of the expression "the greatest science" as a guess of the
longitude from crossing the border of two distinct currents off the coast
(or a guess of the effects of the stream and the wind effects for DR in
general) seems to be exaggerated by Frank. It is undoubtely the great
navigational skill and "art", but a sort of science? Maybe, Slocum had
understood this word in this sense, but I doubt.

The existence of  constant latitude legs in Slocum's narration isn't a proof
that lunars weren't taken. Yes, Moore and Bowditch use lunars for running
from A to B direct way in their examples "The voyage from Portsmouth/Boston
to Madeira", but this wasn't the general method for using them. Lunars were
unreliable to the extent of a half degree of longitude at sea at least,
therefore they were rather used on "constant latitude legs" to verify the
longitude obtained by DR, if used at all. (Frank's interesting reference to
whalers'
logbooks proves it.) There was a discussion about that matter in
the list this year. I haven't the link now, but use ship's name "Arniston"
for finding it, if you like. That ship was lost near the Cape of Good Hope
in early 1800's, because the master hadn't a chronometer and neglected
lunars on the constant latitude leg.

Slocum's mention about the error in logarithmic tables cannot be explained
as a hint at his own error, which he sought to hide by pretext of erroneous
tables. Such tricks are common for beginners that failed the resolve the
task, but Slocum wasn't a beginner and he resolved his task of these unique
clearly attested lunars very precisely after all near Nukuhiva (if he isn't
a liar in your eyes). Some months ago, I supposed for explaining this place
of Slocum's story that Slocum used some "approximate" method for reducing
lunars, as there were errors in various tables of this type. Their value
could be called "logarithm" by Slocum, too, as old navigators used this term
not only for true decadic logarithms of pure trigonometric functions, the
only necessary logarithms in "strict" methods, but also for logarithms of
many auxiliary and sometimes complex values given in special tables. One
look into old explanations for users of these tables can prove it.


Jan Kalivoda

   

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