Atmospheric Electricity

Abstract

THE interesting accounts of certain electrical phenomena of the atmosphere in NATURE of May 16, 23, and 30, lead me to state that it is a common experience of surveying parties, especially on the high peaks and slopes in the western part of this country to undergo these peculiar electrical sensations. In general these may be described as tingling or pricking sensations, accompanied with hissing or crackling sounds, especially marked if a finger be presented to any metallic object near by. But further than this it has been noticed that whenever a flash of lightning occurs there is a sudden cessation of the distressing electrical effects. The explanation of this is, we think, found in some experiments made at the top of the Washington Monument (elevation 500 feet) during thunderstorms. With a “water dropper collecter,” Mascart insulators and quadrant electrometer, we measured the difference of the electrical potential of the air and the ground. The electrometer needle becomes very active with the approach of the “thunder-heads,” and after considerable oscillation begins to move steadily in one direction as if subjected to a steadily increasing “pull,” and then suddenly, when a potential difference of several thousand volts may be indicated, there is an “instant” drop to zero, and apparent rebound in the other direction, not due to the torsion of the suspending wire-fibre. The drop to zero is simultaneous with each flash of lightning. So certain is this relation that we can time the lightning flashes without seeing them. After the flash the needle begins to again move in one direction, repeating its previous behaviour, so that our electrometer measurements seem to prove that every flash of lightning relieves the state of stress of the air, which we may compare with the glass in a Leyden jar, the cloud and ground being the respective coatings.