How Benjamin Franklin Charted The Gulf Stream

Back in the early days of the trans-Atlantic postal service, British packages were taking weeks longer than expected to reach the east coast of North America. With customs officials growing increasingly confused and frustrated at these slow delivery times, it fell to future Founding Father of the United States Benjamin Franklin to solve the problem by creating the first ever nautical chart of the Gulf Stream.

An eastward-flowing Atlantic Ocean current, the Gulf Stream was first noticed by Spanish conquistador Juan Ponce de Leon in the early 16th century. Sailing towards the Caribbean, the famous explorer and his crew found that the current pushing them back was stronger than the wind propelling them forward, thus preventing them from progressing when their ships were in the midst of the Gulf Stream.

By the second half of the 18th century, this vital stumbling block still did not appear on any nautical charts and was apparently unknown to the captains of the British packet boats that carried mail to North America. However, while serving as Postmaster General of British America in 1769, Benjamin Franklin received a complaint from the board of customs in Boston that the packets traveling from England to New York took two weeks longer to arrive than the American merchant ships.

Franklin discussed the matter with his cousin Timothy Folger, who happened to be a whaler and the captain of a Nantucket merchant ship and who explained that while American sailors were generally aware of the Gulf Stream, the British packets were not. According to Folger, these postal vessels often attempted to sail straight through the middle of the Gulf Stream and ignored the advice of American whalers who explained that they would travel much faster if they got out of it.

Using sketches produced by Folger on a nautical chart, Franklin then had the first-ever map of the Gulf Stream printed, with the intention of distributing it among British sailors. Unfortunately, however, his chart was largely ignored by these arrogant navigators, who continued to plot their course straight down the middle of this natural impediment.

A few years later, while crossing the Atlantic as the United States minister to France, Franklin had the opportunity to observe the Gulf Stream for himself, using a thermometer to register its temperature. “I find that it is always warmer than the sea on each side of it, and that it does not sparkle in the night,” he later wrote in a letter to French scientist Alphonsus le Roy.

Based on this observation, Franklin deduced that the air immediately above the Gulf Stream is likely to “receive so much warmth from it as to be rarified and rise,” causing cooler air to be drawn in. All of this, he surmised, may lead to the formation of “tornados and waterspouts”, thus revealing for the first time how ocean dynamics can affect weather systems.

Returning to the issue of trans-Atlantic travel, Franklin wrote in his letter that “the conclusion from these remarks is, that a vessel from Europe to North-America may shorten her passage by avoiding to stem the stream in which the thermometer will be very useful; and a vessel from America to Europe may do the same by the same means of keeping in it.”

Interestingly, this same correspondence includes advice for sailors to always travel with extra personal supplies of wine, cider, rum, and chocolate, but not to bother bringing chickens on board.