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Gary adds:

That is why it would have been better if Wright had started out with
the general method first before showing the special cases.

gl

On Sep 26, 12:35 am, "Gary J. LaPook"  wrote:
> Gary replies.
>
> We can agree that the first two special cases he gives, (the first with
> both points on the same meridian;  and the second case with both points
> on the equinoctial) are trivial with the distance being the difference
> in latitude in the first case and the difference in longitude in the second.
>
> The case you bring up Wright  illustrates with the computation of the
> distance between London and Cape Blanco each having the same latitude of
> 51� 32' north. Because they have the same latitude the general method
> can be simplified but it still works. You start out the same way and
> draw in the points and the lines representing London "B, C, E, and F."
> You draw in the lines and points for Cape Blanco "D, I, K, and L."
> Applying the general method, you set your dividers to the space between
> "L" and "F" and leaving one leg on "F" you swing the other leg to place
> a point on the line "B- C" at that distance from "F" towards "C" just
> like we did in the example with Jerusalem where we plotted "P."  Doing
> it now with the Cape Blanco example let's plot "P2."  Still using the
> general method, we set our dividers to the distance between "K" and "L."
> and set one leg on "E" and placing the other leg on the line "E-F" we
> plot "Q2" just like we plotted "Q" in the Jerusalem example. But wait,
> since the latitude of Cape Blanco is the same as the latitude of
> London, "K-L" is equal to "E-F" so when we plot "Q2" if falls on "F."
> Still following the general method, we use our dividers to measure the
> space between "P2" and "Q2" which turns out to be the same as "F-P2"
> which is the same as "L-F."  So when both points have the same latitude
> we can skip several steps and go right to the circle scale with "L-F."
> Does that help?
>
> gl
>
> George Huxtable wrote:
> >Thanks to Gary LaPook for bringing to our attention that treatise by Wright,
> >and the puzzle his diagrams represent.
>
> >There's been little or no reponse so far, and perhaps that's because others,
> >not just me, have been struggling to understand what's behind Wright's
> >construction.
>
> >I agree with Wright that his first construction, in the case where the
> >departure point and the destination are at the same latitude, gives an exact
> >answer. He proposes a second, different, construction when those latitudes
> >differ. However, if you then apply that second construction to the
> >special-case where the latitudes are in fact the same, it should boil down
> >to the same thing as the first construction. I'm not sure that it does. So
> >I'm not convinced yet that he has got things right. Could there be another
> >typo in his text, perhaps, or in the labelling of his diagram?
>
> >George.
>
> >contact George Huxtable at geo...@huxtable.u-net.com
> >or at +44 1865 820222 (from UK, 01865 820222)
> >or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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