His take on the history of the sextant, its invention by John Harrison (1731), is quite fascinating and he devotes a chapter to its development from Seaman's Quadrants, Cross Staffs and Back Staffs and explains its theory in a post Copernican world view. His narrative history is focused on the voyages of select navigators, going to some effort to describe their personalities and journal anecdotes of his subject, perhaps somewhat romantically. He covers William Bligh (1789), the explorer James Cook (1768), the amusing Bouganville (1766), the unfortunate La Perouse (1785), the under appreciated George Vancouver (1790), Flinders and his cat "Trim" (1796) and the voyages of the Beagle under Stokes (1826) and under Fitzroy (1827). Fitzroy who had quite a practical scientific inclination invited the services of a young naturalist called Charles Darwin (page 225) and achieved a number of social and hydrological accomplishments, including Governorship of New Zealand in 1844.
Barrie ends with two chapters on the experience of Frank Worsely (1916), a merchant seaman from New Zealand, under Sir Ernest Shackleton in an attempt to cross the Antartic continent and their subsequent ordeal of survival. Barrie begins (chapter 4) and ends ( Chapters 15 & 16) his historical narrative with feats of endurance where survivors are faced with navigating though rough open seas in long boats with the threat of eminent danger, that of William Bligh (1789) and Sir Ernest Shackelton (1916). I believe that these narratives serve to illustrate the points he makes on the last pages of his book, that celestial navigation is becoming a necessary lost art. Certainly the average modern human doesn't look up at the night sky with the same comprehension as their ancestors, despite our post Copernican world view.
Inside the book are good illustrations of select navigators, the technologies they used and quite a number of maps, including the Straits of Magellan (Page 250), which Barrie goes to some length to illustrate why they are navigational hazards. It inspires me with a tendency towards looking at the night sky, and to stay away from large bodies of water.