This map was first commissioned in London by Franklin, using coordinates provided by his cousin on his mother's side, Timothy Folger, a merchant seaman from Nantucket. Franklin first published a report for seamen in 1769. He tested the theory during three ocean crossings: traveling home in 1775, traveling to France in 1776, and home again in 1785. With his grandson, William Temple Franklin, he lowered a thermometer into the ocean three or four times a day, recording each temperature. The information was made available in a French edition for merchant and packet boat captains in the months following the Revolution. This map was drawn by LeRouge. It is the third state. A roll of these maps was among Franklin's effects on his death, and is still owned by descendants.
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