Polar Lights *

Abstract

MANY of the principal facts concerning the polar lights, or aurora, have long been known. For example, John Dalton, the great chemist, who observed the lights carefully for many years, and thought deeply upon them, was well aware of their close connexion with the earth's magnetism: as shown by their occurrence mainly in regions centred at the magnetic (rather than the geographical) poles, by their tendency to be extended in the direction transverse to the magnetic meridian, by the near agreement between the direction of auroral rays and the local direction of a freely poised magnetised needle, and by their parallelism, in time of occurrence and in intensity, with magnetic disturbances or storms. His ideas as to their height, on which Cavendish had made careful measurements, were also in general accord with modern determinations.