Mapping the Gulf Stream
Franklin made eight voyages across the Atlantic Ocean (or, as it was known then, the Western Ocean) between the Colonies and Europe. He wondered why journeys eastward were faster than return trips. His curiosity led him to be the first to map the Gulf Stream. The Gulf Stream, along with the North Atlantic Drift, is the ocean current that originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean.
Here is Franklin's original map of the Gulf Stream.