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From: Frank Reed (no email)
Date: Tue Mar 14 2006 - 21:28:26 EST
Jim, you wrote:
"One book I read of late regarding chronometers initially after Harrison's
time commented that a chronometer would cost about 500 pounds sterling, a
sizable sum compared to a ship at about 1500. So, chronometers were
expensive.Then you need at least 3 if you want a reasonably simple way to check how
consistent the rates are holding, so more expense."
Just as an incidental comment here, there were other methods of proving your
chronometer's accuracy, even assuming you didn't do lunars and couldn't
afford multiple chronometers. Ships almost always traded longitudes when they met
on the high seas. Also, there are numerous small islands that can serve as
longitude checks (assuming we are late enough in the 19th century that plotted
positions can be trusted).
And you asked:
"So, that is a long winded approach to getting to the question. What was the
experience with chronometers like for the average seafaring navigator when
mechanical chronometers were the order of the day?"
In America, the dividing line is around 1835 [based on the evidence I have
seen so far. additional evidence might convince me to shift this date but I
very much doubt the shift would be larger than ten years in either direction].
Before this date, most vessels got their longitude by dead reckoning (not
just a rote calculation, but also including other factors) and their latitude by
Noon Sun. On a long voyage, the reckoning might be checked a few times every
two weeks by lunars, but the DR was the "principal" longitude, and
navigators took it very seriously. After about 1835, a majority of American vessels
were starting to carry chronometers. In whaling logbooks from the early 1840s,
it is not uncommon to see references to two chronometers being carried. They
still used lunars in the era, taking them for a few days in a row every two
weeks as a check on the chronometer-based longitude. By 1855 or so, lunars
were essentially history, and chronometers were considered completey reliable
for practical use. As I have mentioned previously on this list, there was
apparently no "lunars era" when lunars were the principal method of getting
longitude. They were always a check, and a very valuable one, on the primary
method, whether it was dead reckoning or longitude by chronometer.
In Britain, and in particular in the Royal Navy, subtract 25 to 30 years
from the dates above. For a specific case, one "Lt. Ashe" writing in 1849 to the
Royal Astronomical Society noted that he had seen only a single instance of
lunars being used to check chronometers in twenty years at sea. Chronometers
were not only widely available in the Royal Navy but widely trusted by 1830.
By contrast, British ocean-going merchant vessels seem to have been closer to
the American schedule.
You also wrote:
"Slocum for example opted for an old tin clock instead of his chronometer
and gives me the impression that on those occasions that he did use celestial
navigation that it was almost as if he were checking his celestial navigation
against his dead reckoning as opposed to the other way round. He was always
confident that he new where he was and how to approach those various
landfalls. He didn't need a fancy expensive chronometer to get by although he was
clearly as familiar with celestial navigation as I would assume most navigators
would be at that time. I get the impression that sailors of the day were more
tuned in to all the elements affecting dead reckoning and relied on it
heavily which may be a bigger reason for the slow acceptance of the LOP."
Yes, that's a good point. Dead reckoning was far more popular and more
successful than many modern navigation histories (mostly anecdotal histories)
would lead us to believe. And navigators believed in their dead reckoning. Even
in the 1850s, I have seen examples of commercial vessels sailing to Java using
nothing but dead reckoning for longitude. As for Slocum, he had an
advantage. He could choose his season and his timing. As Slocum proved, you can sail
around the entire world using nothing but latitude by Noon Sun and dead
reckoning longitude. Of course, if you have to do that every day and you have a
cargo to deliver on schedule, your luck will eventually run out.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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