NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Artificial Sights"
From: Fred Hebard
Date: 2003 Mar 20, 22:24 -0500
From: Fred Hebard
Date: 2003 Mar 20, 22:24 -0500
I apologize for the indirect link to this story; I was trying to credit the source. But Yahoo sites clearly are difficult. Lee Martin gave the direct link previously. As I read the link, the cable-fixing sailors were trying to find the error in their chronometers, similar to the use of lunars, not to synchronize the chronometers. The account is pretty clear that they were working backward from the sights to the time. I would imagine that the location of these cable stations would have been worked out carefully by astrometric means when the cable originally was laid Some of my questions originated from me confusing the timing errors of lunars with the timing errors of straight sights; lunars are less sensitive than standard sights, so that a reading accurate to one second of arc would "only" be accurate to one second of time, not a tenth of a second of time. If they were working backward from a known position, they could get tenth of a second accuracy in time from measurements to the nearest second of arc, to answer one of Lee Martin's questions. But I wonder about reading to the nearest second of arc using a standard sextant. If it were a pillar sextant as George Huxtable describes, that might be possible. All the standard vernier sextants I have seen (mostly on eBay over the last few months) have read to the nearest minute or half minute of arc, with a few going to a ten seconds. And most of the correction labels indicate they were not machined precisely enough to be accurate below ten seconds of arc. I think these sailors might have been using different techniques from those described by Bruce Stark, as they were working in the very late nineteenth century, right before radio, rather than the early nineteenth century. For me, the non-navigational portions of this story were certainly the most exciting. This whole cable business is a great new source of sea stories for me. Fred