telegraph line there is generally a distance such that the curves of
the current undergo no deviation in the vicinity of one of the
electrodes (the only part important for integrations) through the
influence of the other. But it might be admitted that such would prove
the case with a lightning rod in a storm, at the time of the passage
of the fluid into the earth. The ground plate here is one of the
electrodes, and the other is replaced by the surface of the earth
strongly charged to a great distance under the storm clouds. If we
suppose (what may be admitted in a good lightning rod) that there no
longer occurs any spark from the point downward, the curves of the
current, in starting perpendicularly from the ground plate, would be
obliged to leave their rectilinear trajectory and strike the surface
of the earth at right angles. When the electricity flows through a
plane surface into an infinite body, it is only when such surface
presents a very great development that the respective potentials
decrease very slowly in the vicinity of the said surface. No notable
modification occurs, then, in the curves of equal potential, in the
vicinity of the ground plate through the action of this extended
charge, nor consequently any modification in the curves of the
current; but the electricity which spreads has but a short distance to
travel in order to overcome the most important resistances.

The calculations of resistances given above have, then, the same value
for discharges of atmospheric electricity.--_Bull. du Musee de
l'Industrie._

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