NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Longitude by Sunset
From: Alexandre Eremenko
Date: 2012 May 6, 21:32 -0400
From: Alexandre Eremenko
Date: 2012 May 6, 21:32 -0400
Gred, I am very well familiar with Bris sextant:-) I bought the last one from Cassens Plath, and Bill B made truly professional pictures of it: www.math.purdue.edu/~eremenko/Navigation/Sextants/Bris But I don't think it will help much. First, it is designed for Sun, has dark glass, and there is no way to see the Moon through it. One can make another one, of course, with clear glasses, specially for the Moon. But then the advantage that you mention, "one does not need to know the angle" disappeares. And even theoretically, one does need to know the angles. (When timing the settings of the Sun/Moon, the angle is known: it is 0, or more precisely, the refraction angle). I actually do not know how accurate Bris can be. I expect not better than 1'-2'. This is not enough. I have to confess that I have not really graduated my Bris:-( For this one has to spend 5-6 mornings or evenings (sunrise to noon, or noon to sunset) on a sea shore, with excellent weather, and good horizon unobscured in a given direction (W or E). And with my Bris with me:-) I never had such opportunity. (Or maybe had but missed it). I said 5-6 because one certainly needs averaging. I made several observations many years ago, but not enough to graduate the full "scale". Alex On Sun, 6 May 2012, Greg Rudzinski wrote: > > Alex, > > Are you familiar with the Bris type sextant ? A simple version of one of these made from two microscope slides will raise the body above the horizon enough to clear any clouds. Knowledge of the angle is not needed as long as the same device is used to time the horizon set for the Sun and Moon. > > Greg Rudzinski > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- > > > > > : http://fer3.com/arc/m2.aspx?i=119430 > > >