Cause of the aurora.

The Galaxy 7, 1876

Professor Lemström of Helsingfors, Sweden, conceives that the phenomena of the aurora borealis may be explained by similar effects in Geissler tubes. Air acquires its maximum conductivity at a pressure of five to ten millimetres, or say one-seventh to one-fourteenth of the atmospheric pressure. He looks upon the air in the upper regions, where it is rarefied to this point, as forming a great conductor concentric with the earth. The aurora depends upon an accumulation of atmospheric electricity at the poles, where the height of this rarefied stratum is 2,100 miles less, its electric density 9 per cent. greater, and the force of the earth's attraction 42 per cent. greater than at the equator. The aurora results from the combination of this accumulated electricity with that of the earth. But though this theory makes the aurora entirely a terrestrial phenomenon, he also admits the possibility of an intimate connection of auroras and the sun's action.