Weather satellites help modern meteorologists track the movement of storms. All Benjamin Franklin had 250 years ago were observations from here at ground-level. One of his most celebrated observations came in 1743. In Franklin's words: "…there was an eclipse … at nine o'clock in the evening, which I intended to observe; but before night a storm blew up … so that neither moon nor stars could be seen … "

Later, Franklin learned that the eclipse was visible farther northeast in Boston - the storm arrived there after the eclipse ended. With this observation, and observations of several other storms, Franklin deduced that many eastern storms, including the ones we now call nor'easters, approach from the southwest - so they would affect Delaware and southeastern Pennsylvania several hours before reaching Boston.

This motion is easy to confirm now with the view from space, but suggesting it was a major leap during Franklin's time.