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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