Thunderstorm electricity

A recent article by G. C. Simpson [Terr. Mag. 53, 27-33 (1948)] described the remarkable “mirror-image effect.” The effect is illustrated by curves which show that the current from a needle point placed 8.4 meters above the ground at Kew Observatory was negative (that is, a negative potential-gradient existed) when the charge on precipitation particles reaching the ground was positive, and vice versa.Much less refined measurements made by investigators from the New Mexico School of Mines, Research and Development Division, in the spring of 1947 at the top of Sandia Mountain (altitude 10,700 feet) near Albuquerque, New Mexico, yielded similar results. A Wilson electrometer connected to the inner surface of an Erlenmeyer flask having the neck removed and the inner surface sputtered with a transparent but electrically conducting surface of gold was used for the measurement of particle charges. A generating-voltmeter-type field meter was used for potential-gradient measurements. Only qualitative field measurements were sought.