## Abstract

In his theoretical treatment of the deformation and disintegration of individual water drops of undistorted radius R$_0$ situated in an electric field, Taylor assumed that the drop retained a spheroidal shape until the instability point was reached and that the equations of equilibrium between the stresses due to surface tension, T, the electric field, F, and the difference between the external and internal pressures was satisfied at the poles and the equator. He calculated that the onset of instability occurs when F(R$_0$/T)$^\frac{1}{2}$ = 1$\cdot$625, which is in good agreement with experiment. Taylor's assumptions have been applied to the problem of the disintegration of pairs of water drops of identical undistorted radii R$_0$ separated in an electric field with their line of centres parallel to the field. As F increases, the drops deform and eventually one of them disintegrates in a lower field than would be necessary for an individual drop owing to the enhancement of the local field between the drop caused by the mutual interactions of the polarization charges. On the basis of values calculated by Davis for the field enhancement between pairs of rigid spheres, values of F(R$_0$/T)$^\frac{1}{2}$ at the disintegration point were computed. These ranged from Taylor's value of 1$\cdot$625 for large separations to 1$\cdot$555, 9$\cdot$889 x 10$^{-1}$, 7$\cdot$887 x 10$^{-2}$, 3$\cdot$910 x 10$^{-3}$ and 1$\cdot$898 x 10$^{-4}$ for initial separations of 10, 1, 0$\cdot$1, 0$\cdot$01 and 0$\cdot$001 radii respectively. These values of F(R$_0$/T)$^\frac{1}{2}$ are slightly reduced for larger drops owing to the influence of the hydrostatic pressure difference between their vertical extremities. These calculations were tested experimentally on suspended drops and good agreement was obtained. Mass and charge were transferred from the disintegrating drop to its neighbour. Measurements taken from high speed photographs of the radius of curvature and the elongation of a drop at the moment of disintegration agreed quite closely with the predicted values. These studies indicate that the inductive mechanism of cloud electrification will separate appreciable quantities of charge even if the prevailing electric fields are weak provided that a small fraction of the interactions between polarized drops are not followed by coalescence. Numerical values for the elongation of cloud droplets as a function of their separation are presented, which should be utilized in accurate computations of cloud droplet trajectories within electrified clouds. The studies also demonstrate that the local fields between impinging cloud droplets are numerically adequate, even if the external fields are weak, to cause disintegration of one of the droplets, which is generally accompanied by the passage of a filament of water to the other drop, thus penetrating the air film separating the two drops and promoting their coalescence.