On the evening of October 21, 1743 (Julian Calendar), Benjamin Franklin was waiting with great anticipation to view a lunar eclipse. Franklin was disappointed when clouds obscured the sky and a terrible nor’easter set it, blocking his view of the eclipse. The storm wreaked havoc all along the coast from the Mid-Atlantic to New England.
As Franklin read accounts of the storm from newspapers over the next few weeks, he was surprised to find that observers in Boston had been able to view the eclipse before the storm set in. He learned in a letter from his brother in Boston that the storm had arrived there four hours after the eclipse. How could that be?
Franklin observed that winds at his location were from the northeast. He assumed that the storm had come from the direction of Boston since his winds were blowing from that direction. But the storm had arrived in Boston later than in Philadelphia.
Franklin sought other observations from up and down the coast. He put two and two together in a letter to to his friend Jared Eliot, noting that the winds had blown from northeast to southwest, but that the storm had traveled from southwest to northeast.
The wise scientist had come to the revolutionary discovery that the wind in storm systems rotate in a counter clockwise direction around a center that moves across the earth’s surface. A brilliant deduction considering he had no satellite imagery to show him the big picture!
