Letters to the editor

George P. Hobbs´ query in the November 1941 issue of Electrical Engineering (page 562) may be answered on either the practical or the philosophical level. On the former level, the magnitude of the variables is all-important, a fact implied by Mr. Hobbs in his phrase, “a statistical stream of discrete charges.” Since a coulomb contains about six million million million electrons, the calculus applies on a macroscopic statistical basis, within the limits of measurement. On the other hand, in Milliken´s oil-drop experiment we deal with the individual discrete charges, giving rise to the stepwise changes mentioned by Mr. Hobbs, and calling for an entirely different mathematical treatment.