Next message: Alexandre Eremenko: "Integrating marine sextant"
Fred,
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.
Alex.
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
> >>
> >
>
