C.T.R. Wilson versus G.C. Simpson: Fifty years of controversy in atmospheric electricity

Two British scientists, G.C. Simpson and C.T.R. Wilson, held contrasting views on the electrical polarity of thunderclouds for nearly half of the 20th century. Simpson's perspective was dominated by the measured charge on rain, by the breaking drop theory for the charging of raindrops, and later, by the branching behavior of lightning flashes. Wilson's view was dominated by his work on the field changes accompanying lightning, by his knowledge of the corona current from the ground beneath electrified clouds, and ultimately by his unifying global circuit hypothesis, requiring a source current to maintain a negatively charged Earth against dissipation. Simpson's observed tripole structure of thunderclouds provided partial resolution to the controversy, but the main positive dipole supported Wilson's view, which survives today.