An interesting chart depicting the Gulf Stream and thermometric observations of the Atlantic made by American Jonathan Williams, Jr. Williams (1750-1815) was a grand-nephew of Benjamin Franklin and was his personal secretary during the latter’s service as American agent in England in the early 1770s and ambassador to France during the Revolution. He later served the U.S. Army as a senior military engineer, his accomplishments including superintendency of West Point and the fortification of New York Harbor.
This chart accompanied an article by Williams which appeared in 1793 in the third volume of the Transactions of The American Philosophical Society. There he explains how his hydrographic interests developed during his time with his uncle, who made regular thermometric observations during his trans-Atlantic voyages and was one of the first Americans to describe the Gulf Stream (both in text and on a chart). Williams writes:
“In the months of August and September, 1785 I was a fellow passenger with the late Doctor Franklin from Europe to America, and made, under his direction, the experiments mentioned in his description of the course of the gulph stream, an account of which was annexed to his maritime observations, and published in the Philosophical Transactions Vol. II. Page 328, I then determined to repeat these experiments in my future voyages.” (pp. 82-83)
His core finding is that the water temperature tends to decline as one approached banks or shoals if confirmed, certainly a useful finding for mariners. From this he infers that “by noticing the changes in the heat of the sea water, a navigator might always know when he is in soundings, and thereby be able to escape the dangers arising from unexpected currents, and erroneous reckoning.” (p. 82)
Per Wheat and Brun this is the second state of the chart, with the inscription at the top erased and the addition of “Engraved for Williams’s Thermometrical Navigation” at lower right.
Wheat & Brun, Maps and Charts Published in America before 1800, #725. Background on early American Gulf Stream research may be found in Louis de Vorsey, “Pioneer Charting of the Gulf Stream,” Imago Mundi no. 28 (1976), pp. 105-120.
Traces of foxing still evident after cleaning. Folds as issued, with some minor separations mended. Lined.