NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bill Morris
Date: 2010 Feb 14, 12:32 -0800
George mentions Byrd's aeronautical sextant.
Those interested can read about a restoration of one such sextant at http://sextantbook.com/category/aircraft-bubble-sextants/. I surmised that a semi-circular positive lens was used to bring the spirit level into focus at the same time as the heavenly body. There is only one fore and aft vial, with no provision for detecting or eliminating tilt.
Under "Unusual left handed sextant" will be found a post about a later Brandis aeronautical octant, which used a Willson bubble attachment. In this one, the level vial was circular.
Bill Morris
Pukenui
New Zealand.
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