Re: 1st type Hand held Bagnold Sun Compass
From: David Pike
Date: 2020 Dec 3, 14:20 -0800
David Harrison you wrote: Thanks for that informative reply, from the brief mention of the device by Newbold in the RGS Journal I believe it was mainly used like a sighting compass on fixed points & the vehicle mounted compass was the preferred method. From what I can see the expeditions were later in the year also around Oct -November time.
I’m pleased we were able to help you. I think we’ve gone about as far as we can on this for now on NavList. This morning I suddenly thought “I’ll knock one of these together and try it (if the Sun ever comes out again!)”. Then, when I looked at the photos more closely, I realised it’s actually rather clever. The disc must fold over through 270 degrees. Then the backsight must fold up through 270 degrees. The foresight is in there somewhere too. The gnomon must be braised into the 1/8” disc. It’s all rather neat. Mine, if I ever get round to making it, will just be a ‘lash-up’.
You’ll forgive me if I don’t continue testing the formulae for all possibilities of latitude, hour angle, and bearing, but my capacity for finding great things to fill my time at the moment seems to be exceeding my ability to complete it all. DaveP