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More on George's August 2 posting, starting with the second in the series of
questions and remarks:

George: >2. Page 177. Preston refers to Maskelyne's Tables Requisite, which
"describes the calculation of Moon altitudes without explicitly
recommending the use of calculated lunar altitudes for correcting lunar
distances." But one wonders what else, in those days before intercepts and
position lines, a calculated Moon altitude would have been useful for.<

Me: Good point. For my part, I can think of no other use that would have
justified giving them space in a manual of practical navigation.

As for Maskelyne being "on the ball," ABSOLUTELY. He wasn't just a brilliant
astronomer. He also had an extraordinary amount of common sense. The more I
know about the navigation methods and needs of the time, the more I respect
him.

George: >3. Page 178. Preston states, about Lewis- "As he did not have the
three
sextants or octants required for three simultaneous measurements, it is
likely that he used the Problem 4th method ..." [The "Problem 4th method"
is a way of calculating the altitudes rather than measuring them]. I do not
accept this as a valid argument, though the conclusion may be correct.
Although the Navy, overstaffed with officers, might have established a
ritual with three observers and three instruments, it is quite feasible for
the job to be done by one man, with one sextant, measuring in a defined
sequence. That is what Joshua Slocum had to do, single-handed, and so did
countless merchant vessel navigators.<

Me: At sea it's quite easy for one person to take the altitudes before and
after the series of distances. But doing the same thing on land with a
reflecting pool horizon can be a frustrating, blunder-inducing drill. And
there's no need of it. Since the safety of a ship is not at stake, the extra
time it takes to calculate the altitudes is not a problem. The calculation
doesn't have to be done until sometime before the final map is drawn up, and
can be done at leisure. I expect Lewis was instructed not to bother with the
altitudes. In any event, he followed the standard, cut-and-dried procedure of
surveyors and explorers by not taking them.

Enough for now. I'm off to bed.

Bruce

   

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