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    Re: dip, dip short, distance off with buildings, etc.
    From: Bill B
    Date: 2006 Jan 11, 16:14 -0500

    > Bill you wrote:
    > "I have done three trial runs  with the new values, and they seem to approach
    > reality with the average of  mean refraction values derived from the two
    > methods above, a least when  height of eye is 0."
    >
    > Can you elaborate on this 'reality' you speak of?   Seriously, how are you
    > assessing the results.
    >
    > -FER
    > 42.0N  87.7W, or 41.4N 72.1W.
    > www.HistoricalAtlas.com/lunars
    
    
    Sorry Frank, I keep forgetting that there is very little objective reality
    ;-) Perhaps poorly stated, my intent was that the results from both the m^2
    formula and your method come within spitting distance of each other for a
    mean value, and both are almost twice what Bowditch would predict.  With the
    advance in science I would assume we have information not available to
    Bowditch.
    
    As it easier for me to work in feet of rise for my trials, I prefer the
    formula that spits out feet directly.  Modifying from the site you pointed
    out:  nautical miles squared * 0.287= lift in feet.  I did note that if I
    change the constant to 0.265, the results will come within a foot or better
    of your 0.15' per mile/minute guideline as tested calculated from 10 to 100
    nm.  It is relatively easy to convert the constant for values other than
    0.15' if one wishes.
    
    I am still working through your later emails.  In regards to:
    
    "Well, I wouldn't say it that way. The "problem", such as it  is, is that
    the tables in Bowditch are calculated for a specific value of the
    terrestrial refraction --around 0.16 or so."
    
    Referencing your R/(1-x) it would appear the x value in T15 is 0.168.  My
    calculations, *assuming* that your and the web site's methods come close to
    mean refraction as we currently understand it, would be close to x = 0.312.
    
    I'm not dogging Nate, it is just that times have changed, and as pointed
    out, impact traditional navigation.
    
    Back to the beach shots.  Even though the adjusted T15 constants get us
    closer to the 23 nm target (Sears) and 23.5 nm (Hancock) with height of eye
    15 ft and assumed base above water level of 30 ft, both calculations leave
    us short.  Meaning the observed angles were too high by approx 0.8'.  How
    much of this difference be attributed to possible thermal inversion?
    
    Bill
    
    
    

       
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