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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Time sights
From: Alexandre Eremenko
Date: 2005 Jun 1, 13:06 -0500
From: Alexandre Eremenko
Date: 2005 Jun 1, 13:06 -0500
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 > >> > > >