A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2015 Oct 2, 09:45 -0700
I agree with Luc. It's a Blish prism. More details and a patent drawing can be found here: http://sextantbook.com/2012/04/. Bill Morris
It looks like it's the real thing in the 'out of use position' c.f. the patent shetches, which show it in use. So how would you use it to measure dip?
1. Swivel prism forward to the vertical position.
2. Stand where there's a horizon in front and behind you.
3. Remove your cap.
4. look through eyepiece and line up the two horizons.
5. Read value from sextant arc
Q1. Would the arc reading be + or - ? Q2. Should you divide the reading by 2?