A laboratory experiment has been performed to study the relative effect of aerodynamic and electrical forces an small electrically conducting particles of radii 100–200 μ colliding with a particle of 2 mm radius suspended in an upward moving vertical air stream of a wind tunnel and placed in a vertical polarizing electric field. It has been observed, in a low electric field, that the smaller particles collide and move up with the air stream. However, as the electric field is increased, the smaller particles start coming down, after the collision, against the air stream. The electric field required for this change of direction for different particle sizes is higher for the larger angles of collision. When these results are applied to thunderstorms with high electric fields, it is shown that the electrical forces on the charged cloud particles must be taken into account in any consideration of the gravitational separation of charges. Our experimental results indicate that in high electric fields these electric forces can limit and even oppose the further separation of charges.

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