Note 30 — Chapter VI · THE WONDERS OF HEAT: ITS SOURCES.

Professor Challis, of the Cambridge University, calculated the height of the bow of light proceeding from the aurora (seen at Cambridge, March 9, 1847) to be 177 miles above the surface of the earth. The limits of our own atmosphere are placed, by Sir John Herschel, at the 100th part of the diameter of the globe, or, in round numbers, 80 miles above the surface.