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    Slocum and van der Werf
    From: Frank Reed CT
    Date: 2004 Jan 12, 16:41 EST
    In the Spring 1997, in "Navigation: Journal of the Institute of Navigation" there is an article by Siebren Y. van der Werf  of Groningen, Netherlands entitled "The Lunar Distance Method in the Nineteenth Century: A Simulation of Joshua Slocum's Observations on June 16, 1896". Herbert Prinz was kind enough to send me a copy of this article. It's a shame it's not more widely available. Maybe someone could contact the copyright holders and arrange publication on th web.

    Van der Werf's article is more than an analysis of Slocum's observations. It's a meditation on Slocum's use of lunars and a nice general account of the method of lunar distances and the mathematics required to clear a lunar. Van der Werf agrees with my sense that Slocum shot no lunars on his voyage until that June afternoon in the Pacific that Slocum describes so delightfully in his book. He also agrees that Slocum was probably just confused when he talked about discovering an "error in his logarithms". Van der Werf also agrees with some of the people on this list who felt that Slocum probably shot lunars at least occasionally while crossing the Indian Ocean.

    In his article, van der Werf provides an interesting speculation on Slocum's "wrestling with tables". Several people on this list pointed out that Slocum should have been experienced with lunars so any "wrestling" would seem a bit odd. Van der Werf notes that Slocum would never have had a need to do this type of lunar before in which the longitude follows directly from the lunar and a nearly-simultaneous time sight. In all earlier cases, he would have been using lunars to correct a chronometer. So the idea that Slocum might have been confused and might have mistaken his own confusion for the "error in the the logarithms" that he reports is understandable.

    I would recommend van der Werf's article to anyone interested in lunars. It's a nice "meditation" and it's well-written. I don't want to break the Institute of Navigation's copyright, but I think it's within fair use to pass along a photocopy to one other person. Claim it first, and it's yours!

    Frank E. Reed
    [X] Mystic, Connecticut
    [ ] Chicago, Illinois
       
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