NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Latitudes through double altitudes revisited (Bowditch & Benj. Peirce)
From: Joel Silverberg
Date: 2007 Apr 18, 14:07 -0700
From: Joel Silverberg
Date: 2007 Apr 18, 14:07 -0700
I posted a notice on NavList earlier asking for assistance in deciphering the mathemtics behind the method for determining the latitude from measuring the altitude of the sun at two different times and noting the elapsed time behind the observations. Frank Reed was kind enough to direct me to a mid-nineteenth century treatise on spherical trigonometry written by Benjamin Peirce: a friend, student and colleague of Nathaniel Bowditch (and Henry Ingersoll Bowditch, Nathaniel's son, according the the history of mathematics archives at the University of St Andrews, Scotland). Thank you, Frank. Peirce's treatise is a most remarkable resource, and I am looking forward to reading the work in its entirety over the summer. I have tried to organize, clarify, illustrate, and describe Peirce's explanation of the derivation of Bowditch's method and have provided a link to my notes below. I would also like to thank George Huxtable for providing a scanned copy of Cotter's explanation of Ivory's method. The methods are virtually identical, but I found Cotter's diagrams and Cotter's notation to be extremely difficult to follow. For me, at least, they clouded and obscured what was going on, rather than explained what was happening. I have not had the time to see if Ivory's original presentation to the Royal Society is on the web, but I'd be interested to see how Ivory explained things. I would also like to acknowledge the usefullness of the program "Spherical Easel" by David Austin and William Dickinson for preparing the diagrams that accompany this explanation. This program is available as a java applet or as a downloadable program at no cost from http://merganser.math.gvsu.edu/easel/ To see Bowditch's original Rules click on the links http://www.fer3.com/arc/img/bowditchrule.part1.jpg http://www.fer3.com/arc/img/bowditchrule.part2.jpg To see my illustrated explanation of Benjamin Peirce's Derivations of Bowditch's Rules click on http://www.fer3.com/arc/img/benjpeircederivations.pdf Sources: 1825 edition of Nathaniel Bowditch's New American Practical Navigator (pages 247 through 249). 1845 edition of Benjamin Peirce's Elementary Treatise on Plane and Spherical Trigonometry (p. 133,134) both accessible via books.google.com Have fun, Joel --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---