On November 2, 1743 a severe storm struck the American colonies from Virginia northward. The storm might have been a late-season hurricane or strong midlatitude cyclone. It provided some essential insights into the way the weather works.
Jonathan Winthrop
Harvard Science Department
For example, Harvard Professor Jonathan Winthrop recorded the dip in pressure as the storm passed over Boston, making this the first such storm in which barometric observations were made. He also noted the rise in sea level and winds during the storm’s passage.
Benjamin Franklin
National Portrait Gallery
The storm became know as the ‘Eclipse Hurricane’ because it struck on the night of a lunar eclipse. Benjamin Franklin was residing in Philadelphia and was set to make observations of the predicted eclipse, but the clouds from the storm interfered. Franklin observed that the winds accompanying the storm were from the northeast and assumed the storm had come from that direction and so had also interfered with lunar observations made by his brother back in Boston. He was surprised to later find that the eclipse had been visible in Boston and that the storm had struck there hours afterward. Franklin concluded the storm had moved contrary to surface winds. His observations were confirmed by another hurricane which traveled up the east coast of the Colonies in October of 1749, which Franklin was able to trace by using newspaper accounts from various cities along the storm course.
Because of this storm, scientists became aware that storms, rather than being driven by the surface wind, had wind circulations independent of the storm motion. By the early 19th Century, New England scientists began theorizing that storms were, in fact, giant whirlwinds that traveled over the Earth’s surface.