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Posted at 11:02 AM ET, 10/19/2011

Franklin’s storm: How Benjamin Franklin discovered how storms move


Benjamin Franklin (NOAA Photo Library)
Recently, I posted an article about how Ben Franklin’s 1752 invention of the lightning rod was such an important development not only for human safety but also for helping to turn the blind eye of religious extremists toward acceptance of the wonders of science. It was the period, of course, known as the Enlightenment, or the Age of Reason.

In November, 1743, Franklin, who was probably one of the most “reasoned” people of his time, had a huge opportunity to put his reasoning skills to the test. On the night of November 2 of that year --some 268 years ago--an event occurred which cast a whole new light on the movement and structure of storm systems in the Northern Hemisphere (and the world).

Previously, it had always been thought that storms came from the same direction as their surface winds, so it came as a great surprise to Benjamin Franklin when, as a result of a simple astronomical observation and a twist of fate, that this was not the case.

As the story goes, Ben, among his many other pursuits and accomplishments, was an avid astronomer, and was aware that a lunar eclipse would be occurring on November 2, 1743.* He was keenly interested in how this eclipse would appear in Philadelphia, where he lived at the time, compared with the view by his brother (unclear which of his 9 full brothers) from his vantage point in Boston. Therefore, Ben asked his brother to observe the spectacle and provide him with notes.

On the night of the eclipse, Ben was greatly disappointed, as overcast skies and rain had developed, with a brisk northeast wind—some said it was a hurricane. He automatically assumed that his brother would also have missed the event since Boston was hundreds of miles northeast of Philadelphia and would be experiencing the storm first, Ben thought.

Subsequently, Ben received a letter from his brother outlining the details of the eclipse, as viewed in Boston. At the end, he mentioned that the weather turned quite nasty afterward, with rain and gusty winds from the northeast—a real nor’easter.

Ben was obviously quite surprised and perplexed at his brother’s observations. After gathering more data and talking to more observers, he was able, for the first time, to comprehensively document the movement of storms in the northern hemisphere. Years later, in his letter of February 13, 1749 to clergyman Jared Eliot, Franklin conjectures that storms begin to the “leeward,” (meaning that they start earlier in the region toward which the wind is blowing) and begin later to the “windward,” (the opposite direction). Franklin correctly determined that the surface winds of a storm system were only incidental to the forward movement of the storm.

In the above letter, Franklin also contends that a storm is more severe to the leeward, a reflection perhaps of the particular storm in question. As we know today, in the colder months nor’easters often attain their greatest intensity after they pass DC’s latitude**, or to the “windward,” as Franklin would have put it. But if that storm were really a hurricane, it would explain Ben’s belief that nor’easters were more intense to the “leeward,” as hurricanes, particularly late-season ones, often weaken over cooler New England waters. Nevertheless, according to Franklin, this particular storm did cause considerable damage all along the New England and mid-Atlantic coastline, although possibly somewhat less to the north.

*The ability to predict eclipses is thought to have been developed as early as ancient Mesopotamia in the 3rd or 4th century B.C.--John M. Steele, Department of Physics, University of Durham, Durham, England.

**Often around the so-called benchmark position of 40-70, or 40 degrees north latitude and 70 degrees west longitude, where low pressure systems associated with winter nor’easters sometimes attain great intensity and even stall, putting much of New England in prolonged blizzard conditions.

By  |  11:02 AM ET, 10/19/2011

Categories:  Latest, History, Lipman

 
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