estimated that the earth-air current was great
enough to reduce the charge on the earth to one-half its original value
in 10 minutes. McDonald (56) summarized a theory proposed by C. T. R.
Wilson to explain why the earth does not lose its charge. He theorized
that the direction of current flow during fair weather was from the
atmosphere to earth. During storms the direction of flow reversed.
Wilson calculated that there are approximately 3,600 thunderstorms going
on in the world at any one moment. From this and estimates of current
flow during fair and foul weather, he was able to show that a balance of
current flow exists between the earth and the atmosphere. This enables
the earth to maintain its charge.