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    Re: Time sights
    From: Alexandre Eremenko
    Date: 2005 Jun 1, 13:06 -0500

    What I wrote is not COMPLETELY incorrect:-)
    The time spread of signals DID happen.
    And the first short telegram sent DID take
    several hours to transmit (I don't remembr, 6 or 12 hours,
    but of this order of magnitude).
    That they sooner or later found some way to overcome this
    difficulty might be true. But I doubt they knew how to do it
    at the time they layed the cable.
    On Wed, 1 Jun 2005, Fred Hebard wrote:
    > Actually, this is completely incorrect.  One of the first things done
    > with the first transatlantic cable was to transmit time signals to
    > determine more accurately the difference in longitude between North
    > America and Europe.  There are ways of transmitting signals both ways
    > to account for the various delays.  Paul Hirose was kind enough to tell
    > us how this was done a few years ago; unfortunately, I didn't
    > understand the mechanism well enough to reproduce it here.
    > Fred
    > On Jun 1, 2005, at 11:28 AM, Alexandre Eremenko wrote:
    > > I can suggest another reason why time transmission though
    > > a transatlantic (or other very long) cable could not be acceptable.
    > > In those XIX century cables,
    > > the signals were substantially spread in time
    > > when transmitted.
    > > For example, in the very first transatlantic cable,
    > > a short message of few words had to be transmitted
    > > for several hours. A sharp impuls you send from one end
    > > arrived as a very long wave.
    > > So reliable transmission of a time signal could be
    > > impossible.
    > > Alex.
    > >
    > >
    > > On Wed, 1 Jun 2005, Fred Hebard wrote:
    > >
    > >> 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
    > >>
    > >

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