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    Re: Table 8, Bowditch
    From: Lu Abel
    Date: 2009 Jan 13, 00:03 -0800

    Ark Shvetsky wrote:
    > Thank you, Frank!
    > Just wants to make it clear for myself :>: to calculate a distance to the 
    visible horizon I need to use statute miles, not nautical.  Is this a correct 
    No -- the Bowditch formulas are for distance to horizon in nautical 
    As an aside, as Frank pointed out the distance-to-the-horizon figure can 
    vary depending on the amount of refraction, which in turn depends on 
    atmospheric conditions.  Because it's not a three-digit-accuracy 
    calculation, I prefer to use 8/7 as the multiplier rather than 1.15 (or 
    1.17 or other numbers given in Bowditch or other publications over the 
    years).   It's a lot easier to remember and a lot easier to use in 
    mental calculations (and even arguably fewer keystrokes on a calculator).
    > Also, just curious: radio waves and light wave are electromagnetic waves 
    which are differ in frequency.  Therefore, it means the refraction-wise high 
    frequency signal is refracted more.  Is it logarithmic or just a linear 
    correlation for refraction rate between low and high frequency waves?
    The lower the frequency, the greater the refraction.  But there are many 
    factors that contribute to refraction -- for light, it's primarily the 
    density of the atmosphere.  But for lower frequency electromagnetic 
    radiation, its primarily the conductivity of the surface of the earth.  
    So to the best of my knowledge, there's no simple linear-vs-logarithmic 
    Lu Abel
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