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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Bowditch Table 15
From: George Huxtable
Date: 2005 Jan 25, 01:04 +0000

```Trevor's last message ended-

>Jim's web page cites George Huxtable as saying that the second term of
>the Table 15 equation should be included in the square root bracket. I
>am not sure when George posted that information but it might explain why
>
>Maybe George can enlighten us.

===============

Not me, guv. Not that I can remember, anyway. I can't recall pontificating
about that topic; was it some other pontiff? Please quote what Jim's web
page says I said.

I wouldn't have referred to it as table 15, as it's table 9 in my edition.
And in that edition the equation that the table is based on does indeed
have everything included under a square-root bracket anyway.

Transcribed into emailese, and writing A instead of Alpha, the expression
in my edition (1981 vol 2) of Bowditch is-

d = sqr { (tan A / .0002419 )^2 + ((H-h) / .7349) - (tan A / .002419) }

"in which d is the distance in nautical miles, A is the corrected vertical
angle, H is the height of the top of the object above sea level in feet,
and h is the height of the observer above sea level in feet. The constants
.0002419 and 0.7349 are parameters which characterise the effect of
terrestrial refraction."

Is the expression and the text the same in later editions?

To me, it seems a bit suspicious that that text refers to "The constants
.0002419 and 0.7349", although a third, and different, constant of .002419
also appears to be used in the expression. Is that a misprint, I wonder?

Anyway, it has little relevance to Trevor's original question.

George.

================================================================
contact George Huxtable by email at george@huxtable.u-net.com, by phone at
01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
================================================================

```
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