The electric charges and masses of rain drops

The charge (Q) and radius (a) of single rain drops arriving at the earth’s surface have been measured, using a valve amplifier with photographic recording in conjunction with the absorbent paper method for measuring drop radius. The earth’s field (F) and point discharge (I) were also measured. The sign of charge and field were usually opposite. On one day when there was no point discharge the results could be represented by q α – (F+500) where q is the average charge per c.c. and F is in Volts/metre. When there was point discharge the measurements could be represented by Q/I α a or rather by Q/I α a(^2)/V whre Q/I has been averaged for different values of a and V is the terminal velocity of a drop of radius a. It is suggested the connexion between Q/I and a(^2)/V is accounted for by Wilson’s theory of the selective capture of ions by falling water drops. The point discharge current was sometimes observed to lag behind the field at the earth when the field was changing sign.