The search for a reliable and portable method
of determining longitude produced two instruments: the chronograph and the sextant. Dava
Sobel has told the story of the chronograph, and David Barrie has stood up and told the
story of the sextant. Both machines were the result of previous improvements, the
chronograph descending from clocks while the sextant derives from the astrolabe and the
quadrant.
Barrie divides the book into two threads the development and use of
the sextant and his own use of it. Like the chronograph, the sextant is falling out of use
due to the rise of GPS navigation and Barrie felt forced to relate the importance of the
instrument before its use completely disappeared, much like David Lewis did with
Polynesian celestial navigation in The Voyaging Stars. Barries
book works as a moderator to that of Sobels, and proves the case that both
chronograph and sextant were necessary for an accurate longitude placement.
The style of Sextant is such that it is an easy
read. Barries personal experience with the sextant gives him a degree of authority
necessary to explain its workings and uses. He then proceeds to highlight some of the more
extreme situations the instrument had been used in. Due to it being used primarily with
naval navigation, these situations usually involved strong winds and icebergs or roughing
it in the Pacific. The navigators Barrie selects to highlight the importance of the
sextant Bligh, Frank Worsley, Joshua Slocum, Flinders et al. - may not all
be famous for navigation, but therein lies the vagaries of history.
The text is generally easy to read, and Barrie has provided a decent set
of illustrations and maps to illuminate the text. There are also two sets of plates
covering both the historical journeys as well as Barries voyages. All that is needed
now is a volume on the men and women responsible for providing the data and observations
without which both the chronograph and sextant were useless. But that really is a nerdy
subject.
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