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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Bowditch 1926
From: Chuck Taylor
Date: 1996 Sep 03, 11:43 EDT
From: Chuck Taylor
Date: 1996 Sep 03, 11:43 EDT
Over this past weekend I was browsing in a used book store in Port Townsend, WA (USA) and was lucky enough to find a copy of the 1926 edition of Bowditch. I couldn't resist. A few comments about the way things apparently were 70 years ago: 1. The sextant described was of the clamp-screw vernier type, calibrated to 10 seconds of arc. There was only passing reference to the "new" micrometer drum sextants being introduced in the U.S. Navy. 2. Altitudes were measured in degrees, minutes, and seconds and the computations were carried out accordingly (rather than in degrees, minutes, and tenths of minutes). 3. The organization by chapter says a lot about the way navigation was practiced then. There are successive chapters on Chronometer Error (Time Sights), Latitude, Longitude, Azimuths (compass checking), and Sumner Lines. The altitude-intercept method of St. Hilaire is mentioned in a subsection of the chapter on Sumner Lines. Apparently finding your latitude and finding your longitude were viewed as separate, discrete processes. The positioning of chapters would suggest that lines of position were regarded as somewhat less important. 4. Sight reduction relied on tables of trigonometric functions and logarithms. The basic Law of Cosines was arranged in several different forms to facilitate different methods involving the usual trigonometric functions (sines, cosines, etc.) plus haversines. All the necessary tables, including logarithms of the trigonometric functions, are provided. The only operations required besides table lookup are addition, subtraction, and division by 2. The tables, like most tables today, are to 5 decimal places. (I wonder how long that has been going on?) 5. At least one table was calibrated for courses given in points. There was an equivalent table for courses in degrees. 6. The section on chronometer error mentions "recent" advances which allow chronometers to be calibrated by telegraph. They had a system where a signal was sent first one way, then the other, to account for signal lag. It also mentioned "time balls" (like Times Square on New Years' Eve) as being common. 7. The original price was $2.25. 8. It mentioned that prior to 1926, almanacs were set up to measure days from noon to noon, not midnight to midnight. I hope this is of interest to at least someone else on this list! :-) Regards, Chuck Taylor Everett, WA, USA ctaylor@XXX.XXX ------------------------------------------------------------------------ This mail list is managed by the majordomo program. To from this list, send the following message to majordomo@XXX.XXX: navigation For help, send the following message to majordomo@XXX.XXX: help Do NOT send administrative requests to navigation@XXX.XXX -ben ------------------------------------------------------------------------