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The time sight has been always employed in checking chronometers in any
situation wherein the Longitude might be accurately known, i.e., when
passing accurately charted headlands, lighthouses, etc., or at any other
times that a position might be plotted based on accurately charted
entities. Normally such accurately charted entities were established by
hydrographical surveyors, as they were called, in the employ of various
maritime nations, including GB and the USA amongst others, or had been
otherwise established by qualified mariners as a public service - I have
never heard these folks referred to as astronomers and personally believe
calling them such to be a misnomer. Obviously, the difference between
true and calculated longitudes is related to the chronometer error,
whether one chooses to reset or simply rate the instrument. Incidentally,
before the advent of wireless telegraphy, signal stations that were able
to maintain correct time by landline telegraph were also communicated by
passing ships for this purpose and the correct time signaled by flag
hoist . Checking the chronometer by observations in accurately charted
locations was indeed so common as to be an included discipline on license
exams of yesteryear.
Henry
On Wed, 1 Jun 2005 09:52:41 -0400 Fred Hebard <> writes:
> In reading the Wikipedia entry on celestial navigation, I came across
> the following statement:
>
> "Traditionally, a navigator set his chronometer from his sextant, at
> a
> geographic marker surveyed by a professional astronomer. This is now
> a
> rare skill, and most harbor masters cannot locate their harbor's
> marker."
>
> A few years ago, in discussing a late 19th-century book about repair
> of
> submarine telecommunications cables, I asked why the captain and
> first
> mate went ashore to do time sights, when the could have gotten time
> from the cable. I suppose the answer was that time wasn't sent over
> the cable that often, not to mention that it might have been broken
> when they were in harbor. At any rate, this is the first mention I
> have of people setting their chronometer from a precisely measured
> location. Previously, I had gather from this list that the captain
> and
> first mate were rating their chronometer, not setting its absolute
> time. It appears they were setting it, and perhaps also rating it.
>
> Is there any mention of this in the older texts, such as Chauvenet,
> where time sights were done at geographic markers set by a
> professional
> astronomer?
>
> Thanks,
>
> Fred
>
