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| STURM, Leonard Christofle,
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| Project de la resolution du fameux probleme touchant la longitude sur mer
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| Nuremburg: Pierre Conrad Monath, 1720
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| First edition.
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| Small 4to. Large hand-colored folding plate at end.
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| Vellum over boards.
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This is a curious early work attempting to address the problem of finding longitude at sea. In the early 18th century no marine chronometer existed and the astronomical techniques pursued by Galileo, Cassini, and others were difficult to use and gave poor accuracy. Consequently the prevailing method of finding longitude at sea was dead reckoning, which consisted of measuring the elapsed distance that a ship had traveled over the surface of the water. This was typically done by measuring its surface speed. The method was plagued with inaccuracies, the most notable of which was due to the effects of prevailing ocean currents. If one didn't have a good local measurement of the speed of the current, then dead reckoning would arrive at an inaccurate measure of the absolute speed of the ship with respect to longitude.
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Sturm's invention was a variant on dead reckoning that was essentially a marine odometer consisting of a large water wheel of precise design that would directly measure the surface distance traversed by the ship. The design of the invention is shown in a very large hand-colored plate bound at the end of the book.
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