Next message: Frank Reed: "Re: Gavin Menzies and "1421""
Bill, you wrote:
"To follow up on your use of a 0.15 constant (R/(1-.15) for
calculating dip, short dip etc., one might question the entire system. "
You bet. The entire system depends on a very specific choice for the value
of terrestrial refraction. Don't get me wrong, the choice in Bowditch is
certainly a good one "on average" --if you have to pick one value, you couldn't do
much worse. But how much should a navigator trust those tables? This is the
really interesting matter. If I look up a dip short value, or if I estimate a
distance from Table XV, what kind of confidence can I have in the results?
That "on average" choice in Bowditch could be very wrong in fairly common
atmospheric conditions. There are coastal locations where significant temperature
inversions occur each and every day, and these definitely have a big impact
on the numbers in the tables.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
