NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Preston's paper on Lewis & Clark's Navigation
From: Fred Hebard
Date: 2003 Jun 7, 10:46 -0400
From: Fred Hebard
Date: 2003 Jun 7, 10:46 -0400
In the thread on Maskelyne's tables, George Huxtable very kindly provided a link to the late Richard.S.Preston's paper,"the accuracy of the Astronomical Observations of Lewis and Clark", downloadable from www.aps-pub.com/proceedings/jun00/Preston.pdf. I read this with great interest, but have some questions. In the table at the end of the paper, I note that the Lewis & Clark latitudes all seem to be out by about 5' of arc. Is this a large amount of error? It would seem those measurements could be more accurate. I presume Preston used modern ephemerides to calculate the positions, but wonder whether the old ones were accurate enough to get closer than 5', which then would influence the care with which the observations were made. Bruce Stark has mentioned that he also has become involved in working up some of the Lewis and Clark lunar data. From the description in Preston's paper, it sounds as if Lewis and Clark took lunars almost daily, but Preston summarizes only 20 or so observations. I wonder whether access to the raw data is possible. Does Preston accurately describe the old methods of using an assumed longitude to start iterating toward a more accurate one when simultaneous altitudes are lacking? It would certainly appear so from his description. Our esteemed George Huxtable apparently came to a fuller understanding of these calculations more recently, so I wonder how Preston stacks up. I must add a word of thanks to Ken Muldrew for stirring up an interesting discussion and prompting George Huxtable to repost the link to Preston's excellent (as far as I can tell) paper. Fred Hebard