On the evening of October 21, 1743, Benjamin Franklin was waiting with great anticipation to view a lunar eclipse in Philadelphia. 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 the direction of Boston. But the storm had arrived in Boston later than in Philadelphia. Franklin sought other observations from up and down the coast. Interestingly, the winds had blown from northeast to southwest, but that the storm had traveled from southwest to northeast.
In a letter to Alexander Small that Franklin penned on this date in 1760, he described the experience of the aborted lunar eclipse. Franklin assumed that the storm had blown in from the northeast because the surface winds at his location were northeasterly. He was puzzled to find out later that his brother had viewed the eclipse with no problems and that the storm had arrived in Boston four hours later. The information caused Franklin to surmise that the storm had moved from southwest to northeast. Franklin 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. It was a brilliant deduction considering he had no satellite to show him the big picture!
