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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
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