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Nathaniel Bowditch The Practical Navigator
Salem’s irascible little “arithmetic sailor” made seamanship a science and left all mariners in his debt
August 1960 | Volume 11, Issue 5
Three items were often listed ax essential in the sea bag of every youngster who heeded the rail of blue-water ships and wandered down the long road to the nearest port: a knowledge of the Gospel, a pair of woolen socks knitted by his mother, and a book— The New American Practical Navigator . The ascending order of importance was never questioned. The Gospel might in time of peril provide confusing answers, and the socks develop holes, but the book would never fail. It would lead him anywhere on earth and bring him home safely and surely across the trackless ocean.
This was not always so.
Around the end of the eighteenth century, something like an uneasy truce existed between the townspeople of Salem, Massachusetts, and an irascible young man named Nathaniel Bowditch. He had a way with figures the like of which nobody in Salem had ever seen, and if he had stuck to his sums in the ship chandlery where he worked, he and Salem might have gotten along quite nicely. Bowditch, however, was not a man to hide his talents. He was eager, almost before anyone asked, to demonstrate his mathematical skill—often by proving how he had discovered an error in Sir Isaac Newton’s Principia Mathematica —and if the listener couldn’t follow the calculus, he was likely to be called a stupid dolt. This attitude made Bowditch few friends, but it wasn’t until he set himself squarely against the maritime dogma of the times and challenged the authority of practical men that he stirred up real opposition. Hut he also proved that he had the finest mathematical mind in America, if not the entire world. What he bequeathed to succeeding generations—his New American Practical Navigator —is proof of his genius.
Bowditch insisted that mathematics does not lie. He said that if two and two made four on land, it was equally true on a ship a thousand miles at sea. He committed the heresy of proclaiming that mariners should navigate their ships precisely by mathematics and celestial observation instead of trusting to practical experience and luck, ff they would only put their faith in the unvarying stars, so this land-bound book-keeper said, ships would reach their destinations more swiftly and safely.
The problem of determining exactly a position on the surface of the globe was one that had long baffled seafaring men. There was nothing new in Bowditch’s idea of celestial navigation. Steering by the stars had been practiced for countless centuries, but there was a vast difference between this and using them to calculate a precise position. By the late 1700’s, rough instruments and calculations had been worked out for finding one’s position on land, but it was a lengthy and laborious process, requiring a great deal of astronomy and mathematics as well as a means of knowing the exact time. Furthermore, the final results were not truly accurate.
In navigating a ship certain things were possible, ot course. Distances run could be determined by dead reckoning—that is, by measuring the miles traveled through the water and then applying this figure to known compass headings. In beating into the wind, however, where the vessel sideslipped through the water, or in sailing through unknown currents and tides, dead reckoning was liable to grave errors.
A ship’s latitude could be determined by celestial observations if the mariner was up on his mathematics and had good instruments on board. Taking altitudes on the sun and moon, and sometimes on such stars as Polaris, Sirius, or Vega, had enabled generations of pre-nineteenth century sailors to establish distances north or south of the equator.
Navigation in those days was actually a pretty rough and ready business. Such refinements as were known for establishing “fixes” were far too complicated lor the rugged seamen who walked the poop decks of merchant and navy ships of the period. Captains took their vessels out and—it they were lucky—brought them home by “seaman’s eye” and “seaman’s feel”: the smell and feel of the wind, the look of the sky, the color of the water, the characteristics of the ocean floor far beneath them. Experienced navigators could take sights on the sun and moon and, by following the selected latitude across the ocean, make a reasonably accurate landfall. Bad weather or contrary winds could complicate the navigator’s task, however, and he still had no reliable method for determining a position in longitude—his distance east or west of the prime meridian at Greenwich, England.
By 1800, the need lor more accurate navigation had become acute. The navies of the world were dividing the earth into far-reaching political and commercial empires; demands for raw materials were soaring; industry was producing surplus goods that commanded enormous profits abroad. Shipbuilders were turning out larger vessels capable of safely carrying heavier and more valuable cargoes. Time was money and power—fortunes awaited the ships that got there first with the most.
Everything was ready and waiting, except that men still did not know how to navigate properly. Voyages that should have been accomplished in weeks took months, and those that should have been completed in months sometimes took years.