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The Historical Importance to Navigation of Nathaniel Bowditch’s New American Practical Navigator                            

Remarks at a celebration on 31 October 2017 at the Headquarters of the National Geospatial-Intelligence Agency, Springfield, Virginia, of the publication of the 2017 edition of The

American Practical Navigator

            On 20 November 1820, on the South Seas whaling grounds some two thousand nautical miles west of South America, an unusually large and aggressive sperm whale rammed the small Nantucket whale ship Essex, staving in its bow. As the twenty-man crew abandoned the sinking vessel, some 1,200 miles from the nearest known islands, Captain George Pollard Jr. saw to it that they took with them the tools they would need to navigate their whaleboats to a safe landfall: compasses, quadrants, and “Bowditch,” as Nathaniel Bowditch’s New American Practical Navigator had come to be known. First published in 1801 (but with an 1802 imprint), by the 1820s Bowditch’s guide to navigation had gained a universal presence aboard American vessels and U.S. Navy midshipmen learning their profession had come to refer to the work as “the immaculate Bowditch.”

            What accounts for the popularity of Bowditch, its victory over its rivals in the early nineteenth century, and its continual usefulness as a guide for navigators? That the work’s orientation was practical, rather than theoretical, designed to be useable, training sailors to navigate rather than educating them in the mathematical theories behind the methods, helped make it a best seller. But its early popularity was not owing to any originality in producing a practical rather than theoretical navigation manual. That innovation had been made by the Englishman John Henry Moore, with his New Practical Navigator, first published in London in 1772. Bowditch’s easy-to-use method of taking and working a lunar observation, an advanced technique for determining longitude, added to the attraction his book held for sailors. Yet the New American Practical Navigator did not originate the lunar method of calculating longitude, since a number of such methods had preceded Bowditch’s. Bowditch made his manual even more attractive to navigators by providing pre-computed tables that simplified the calculations required by the lunar method. Yet, again, this was no innovation of Nathaniel Bowditch’s, for Nevil Maskelyne, Britain’s Astronomer Royal, had done this first.

            The chief improvement of Bowditch’s New American Practical Navigator over Moore’s New Practical Navigator was not in any innovation. Rather, it was in the greater reliability of its navigational tables. “Ultimately what mattered,” as Bowditch’s biographer, Tamara Plakins Thornton, says, “was the reliability of the numbers.” The exactitude of Bowditch’s mathematical calculations set his guide apart. Bowditch recalculated and corrected thousands of mathematical values found in Moore. Errors in Moore’s tables were known to have led to fatal navigational mishaps, but sailors found they could safely stake their lives on Bowditch.

            Nathaniel Bowditch, born in Salem, Massachusetts, in 1773, took a delight in numbers, finding in them the certainty, even moral certainty, he discovered missing elsewhere in the world he knew. In contrast to most others, even professional mathematicians, Nathaniel found doing complex calculations immensely satisfying. By the time he was a young man, his reputation for making complex calculations was well established. So, it is unsurprising that in 1797 Edmund M. Blunt, publisher of The American Coast Pilot, wanting to publish a new edition of Moore’s New Practical Navigator, then in its twelfth edition, sought out Bowditch to revise it.

            Determining latitude—how far north or south of the equator one is—is relatively straightforward using a sextant to measure the angle of the sun above the horizon at noon. The problem was how to determine one’s longitude, how far east or west of zero degrees, the prime meridian, set at an agreed-upon location, such as Greenwich, England, the site of the British Royal Observatory. You may have read Longitude or seen the movie based on the book, Dava Sobel’s story of John Harrison’s invention of the chronometer, a time piece that keeps accurate time despite the tossing and turning of a ship at sea. The chronometer allows the navigator to know the time of day at the prime meridian and to compare it with noon, when the sun is at its zenith, where the ship is. Every four minutes’ difference between noon where the ship is and the time at the prime meridian equals a degree of longitude. Thus, if it is noon aboard a ship crossing the Atlantic Ocean and 4 pm in Greenwich—that’s 60 minutes to the hour, times 4 hours equals 240 minutes, divided by 4 equals 60—the ship is at sixty degrees west. But if you cannot afford a chronometer—and at the start of the nineteenth century the instruments were so expensive that few merchants made the investment—the alternative method of determining longitude was a system of working lunars.

            Working lunars uses the moon much as the hands of a clock moving against the background of the sun, the stars, and the planets. In taking a lunar, the navigator uses a sextant to measure the angle of the moon with other heavenly bodies, the sun, stars, and planets. The shipboard time of the observation is then measured against the time that the same angle would have occurred at zero degrees longitude. The difference in time would be converted to the difference in space. If it were as simple as this, the result would give the ship’s longitude. But three factors complicate the calculation. The first factor is the inaccuracy inherent in using a sextant, inaccuracy that could be minimized by increased skill in the user. The second and third complicating factors are the bending of the light coming from heavenly bodies as it passes through the atmosphere and the fact that the measurement is taken from the surface of the terrestrial orb rather than from its center. Correcting for these latter two factors requires a complex series of trigonometric and logarithmic calculations. Pre-calculated tables can simplify the mathematical calculations.

            Moore’s book contained pages of tables for converting the lunar observations into positions on the globe. Errors populated Moore’s tables and Bowditch’s greatest contribution was the accuracy of the revised tables, based on thousands of new calculations he made, calculations others, even those having the skill, lacked Bowditch’s exceptional patience, dogged determination, and deep devotion to accuracy to make.

            Bowditch’s revisions to Moore’s work were so extensive, correcting some ten thousand values, that his publisher, Blunt, issued the manual as an original work under Bowditch’s name.  Bowditch updated and revised the work eight times before his death in 1838, working with the publisher to ensure accuracy of the printed volumes. –As an editor of historical texts, I am acutely aware of the importance and drudgery of precise proofreading and can imagine the care it took to check the accuracy of the typesetting of all those numerical tables.

            By the 1820s chronometers were becoming more affordable and these time pieces were appearing more frequently aboard merchantmen. The presence of chronometers on shipboard diminished the value of Bowditch’s lunar tables—yet whenever the chronometers ceased functioning, those tables regained their usefulness. Even with the replacement of the lunar method with chronometers for determining longitude, Bowditch’s manual retained its popularity because of numerous improvements the author made—aside from the accurate lunar tables—that enhanced its usability and usefulness. For example, Bowditch included information and data useful for conducting trade in the increasingly impersonal global marketplace: instructions for calculating compound interest and for understanding marine insurance coverages; explanations of the workings of bills of exchange and commercial contracts; laws as they related to a ship’s owners, masters, factors, and agents; and examples of commercial forms and captains’ accounts. His American audience found the increased number of American ports for which Bowditch listed the precise longitude and latitude a valuable addition.

Before 1845, with the founding of the U.S. Naval Academy, the training of midshipmen took place principally on board ship. As a navy commander in the Antebellum Navy, the future Admiral Samuel F. DuPont described midshipmen preparing for their examination to become passed midshipmen, eligible for promotion, “with a Practical Navigator as their sole instructor and a campstool between two guns, for their study room.” The Rare Book Room of the Navy Department Library holds copies of several early editions of Bowditch, including two of the first edition. Among these volumes are three that bear evidence of their use as training manuals for navy midshipmen. The 1817 edition in the collection has inserted into it the frontispiece— a fold-out map of the Atlantic Ocean—and the 1817 title page to which the map is attached. These pages have been saved from a copy of the 1817 edition different from the book itself, which is intact and has its own frontispiece and title page. The loose map and title page have the notation in ink, “I made of a cruise in the US ship Macedonian . . . Mid’n Alexander Slidell,” along with a geometric figure in pencil and a couple of trigonometrical calculation of degrees, minutes, and seconds. Slidell received his appointment as midshipman in 1815. Later, he would change his name to Alexander Slidell Mackenzie and would become infamous for his role in the Somers affair, in which the son of the secretary of the army was hanged for mutiny. The 1821 edition of Bowditch in the collection has the dedication, “Murray Mason from his brother Mason Jr. New York July 21st 1824.” Mason, a grandson of George Mason, father of the Bill of Rights, had received his midshipman’s warrant seven months earlier, on 14 November 1823. This volume contains evidence of study, for paragraphs scattered throughout are marked off in pencil, while there are notations in ink regarding logarithms, astronomy and geometry, preparations for making lunar observations, how to find the latitude by the altitude of the sun, and the calculations needed to use a chronometer correctly. The 1826 edition in the collection had been passed on from John Henry Sherburne Sr., who became register of the Navy Department in 1825, to his son, John Henry Sherburne Jr., probably in 1829 when the latter became a midshipman. The Sherburne volume has paragraphs marked off in pencil, like Mason’s volume, but instead of ink notations written directly on the pages, numerous full, half, and quarter sheets of paper tipped in and bearing notations on various navigational procedures. The volume also bears evidence of occasional boredom with study: doodles and irrelevant statements, including this exclamation, “Oh give me great ocean room.” The volume was apparently treasured in the family, for in 1903, according to a notation in the book, it was given to Sherburne S. Hopkins, evidently a Sherburne descendant.

Up until just about the time of Bowditch’s death in 1838, the New Practical American Navigator provided the Navy’s midshipmen with their principal book training in navigation. But in 1836, Navy Lieutenant Matthew Fontaine Maury, who would later earn the sobriquet “Pathfinder of the Seas” for his pioneering work in oceanography, published a new work for educating midshipmen in navigation. Maury underscored the difference of his approach with that of Bowditch by calling his book A New Theoretical and Practical Treatise on Navigation. With others in the Navy besides Maury believing that midshipmen would benefit from understanding the theory behind the practice,  midshipmen were soon studying Maury’s book instead of Bowditch’s and Maury’s would become the text of choice at the Naval Academy.

            In the merchant marine, however, practical value retained its priority over theoretical understanding.  In 1834, when Harvard College student Richard Henry Dana Jr. sailed before the mast in the merchant brig Pilgrim on a two-year journey to restore his eyesight injured by a case of measles, he sought to educate himself on navigation by mastering Bowditch. He recorded in Two Years before the Mast, his famous account of the voyage from Boston to California and back: “Then I took hold of Bowditch’s Navigator, which I had always with me. I had been through the greater part of it, and now went carefully through it, from beginning to end, working out most of the examples.”  Contemporary with Dana’s voyage by sea to the West Coast, one of Dana’s fellow Bostonians, Nathaniel J. Wyeth, was leading expeditions of easterners to settle Oregon Territory.  Wyeth explained in a letter in 1834 how to apply Bowditch’s navigation instructions to finding one’s way across the trackless West. Thus it was not only those who sailed the seven seas but also those who navigated prairie schooners across the North American continent who found Bowditch a practical guide.

            On 3 May 1866, the Hornet, an American clipper ship in the San Francisco trade, caught fire a thousand miles west of the Galapagos Islands. With its cargo of candles, case oil, and oil in barrels promising to turn the ship into a raging inferno, the crew of twenty-nine officers and men and their two passengers abandoned ship in three open lifeboats. Forty-three days later, the captain’s boat fetched ashore on the Island of Hawaii bearing fourteen survivors, but the other two boats, which had separated, were never heard from. Samuel Clemens, better known as Mark Twain, who was on the island as a special correspondent to the Sacramento Daily Union, helped preserve the record of this event by interviewing survivors and publishing their story in his paper.  Twain portrayed the master, Captain Josiah A. Mitchell, as a heroic leader. As the men had prepared to leave the burning ship, Mitchell took account of their navigational tools. Of the three compasses, one was small and toy-like. There were only two chronometers for the three boats. Each boat had a sextant, and like the whaleboats of the sinking whale ship Essex, each boat took with it a copy of Bowditch. That the sailors of two vessels in the midst of the Pacific Ocean lost to disasters separated by forty-six years looked to Bowditch for their salvation signals the universal presence, the longevity, and the perceived value of this useful work.

In 1866 the United States Hydrographic Office purchased the copyright, and the U.S. government has kept the work in continuous publication. Few changes were made in the text between Bowditch’s death and 1880, when a thorough revision was made under direction of Commander Philip H. Cooper, USN. Between 1946 and 1958 another set of major revisions was made, since which recurrent revisions—dropping obsolete material, reorganizing chapters, and adding new material keeping pace with changes in electronic navigation—have kept the work up to date. According to a current commercial advertisement for the 2015 edition of The American Practical Navigator, “during the last two centuries over 75 editions, almost 1,000,000 copies, of Bowditch have been published by the US Government. It has lived because it has combined the best technologies of each generation of navigator.”

            The National Geospatial-Intelligence Agency is to be congratulated on publication of its newest edition of this venerable and most practical epitome of navigation.

Michael J. Crawford

Naval History and Heritage Command

Published: Wed Nov 29 13:31:01 EST 2017