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Under ordinary conditions the electricity of the air is positive in relation to the ground and the oceans. Its potential does not vary greatly, being rather higher in winter than in summer—a change which might be considered normal. During rainfall or snowfall the potential usually is unsteady, varying rapidly between positive and negative. The changes are quiet; in ordinary cases they can be detected only by means of sensitive electrometers designed for the purpose.

Ether Waves.—From time to time there are sharp but slight variations in the electric potential both of the earth and of the air. The former are created by the “earth currents” which, in the time when the telegraph was operated by grounded battery circuits, were the bane of the telegrapher. The sharp variations of the atmospheric potential are known as “static waves,” or “ether waves”; they are the most common obstacle in radio-telegraphy and telephony.

The ether waves of atmospheric electricity apparently have little or no effect upon the activities of life; they also seem to be unimportant to meteorology, except as their increasing frequency may possibly indicate the approach of a thunder-storm. Ether waves of the Hertzian type, caught at a distance