Benjamin Franklin: In His Own Words
Transcript of "Suppositions and Conjectures on the Aurora
A Similar Operation is perform'd by Nature on the Air of this Globe. Our Atmosphere is of a certain height, perhaps at a Medium Miles. Above that height it is so rare as to be almost a vacuum. The Air heated between the Tropics is continually rising, its Place is supply'd by northerly & southerly Winds which come from the cooler Regions.