Our knowledge seems rather to point to the
substances upon which the charges are collected. The self-repellent nature
of electricity compels it to manifest itself at the more prominent parts
of the surface, the level being forsaken for the point. The tension of the
charge, or its tendency to fly off, is proportionately increased. And if
at a given moment the tension attains a certain intensity, the discharge
follows, emanating from the surface which offers the greatest facilities
for escape. The earth is generally flatter than the cloud, whence, in all
probability, the discharge more frequently originates with the cloud.
Should a lightning flash strike the earth and produce direct neutrality,
it is possible that no damage will result, although this again is not
always certain, because when the cloud charge acts inductively on the
earth it produces the opposite (say negative) charge on the nearer parts,
the similar (or positive) state is also produced at some place more or
less distant. Sometimes this "freed" positive (which, by the way,
accumulates gradually and physiologically imperceptibly) is collected at
some portion of the earth's surface. When the negative is neutralized by
the discharge, the freed positive is no longer confined to a particular
region, but tends to dissipate itself, and a shock may be felt more or
less severely by any person within the region.
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