NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Certaine Errors in Navigation Corrected
From: Gary LaPook
Date: 2007 Sep 26, 00:41 -0700
From: Gary LaPook
Date: 2007 Sep 26, 00:41 -0700
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. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---