NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Anomalous dip. was: [NAV-L] Testing pocket sextant.
From: George Huxtable
Date: 2006 Jun 16, 21:00 +0100
From: George Huxtable
Date: 2006 Jun 16, 21:00 +0100
I've just posted a meassage, in the hope of reducing misunderstandings, in which was the paragraph- | When you observe a highway surface on a hot day, you can see a bright | "pool" on the surface, which is an image of reflected sky. But this is | NOT reversed dip, it's locally ENHANCED dip, in the normal direction | of dip. It implies that even looking somewhat downward, into the | highway ahead, you are still seeing the sky, and you have to look more | downward still until you see a view of the ground, at an enhanced | angle of dip. That's because the temperature gradient over the tarmac | is hotter below, warmer above (the opposite way round to what we are | hypothesising occurs over a sea surface). There is no inconsistency. The hope of achieving clarity was in vain, when I write such confusions as "the temperature gradient over the tarmac is hotter below, warmer above". What I should have written, of course, was- "the temperature gradient over the tarmac is hotter below, cooler above". Now, I hope that's a bit clearer. George contact George Huxtable at george@huxtable.u-net.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
