NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Timing Lunars with a Rock
From: George Huxtable
Date: 2005 Jul 19, 09:44 +0100
From: George Huxtable
Date: 2005 Jul 19, 09:44 +0100
Come on, Bruce, your memory is as bad as Jared's, when you write- >The old navigation manuals suggested checking the log line and half minute >glass occasionally. One way to check the glass was by pendulum. As I >recall, the length of the pendulum, to the center of the musket ball that >formed the weight, was sometimes given as 29 and 1/4 inches, and sometimes >as 29 and 1/8. Count a second each time the pendulum passed the bottom. I >suppose you had to give the pendulum a few moments to settle the length of >its swing. > >Bruce It's not 29 and-a-bit, but 39 and-a-bit inches, which I have just confirmed by working it out from the expression for a period of 2 seconds as 2 x pi x sguare-root-of( length / gravity acceleration ). And to be doubly sure, I've just checked it against the pendulum of my old grandfather clock in the hall. 39 and-a-bit it is. What a mess listmembers would make of estimating time at an African lake, if that's the best they can do between them! George. =============================================================== Contact George at george@huxtable.u-net.com ,or by phone +44 1865 820222, or from within UK 01865 820222. Or by post- George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.