Experiments and Observations on Electricity Made at Philadelphia in America

By Benjamin Franklin

Page 40

fire must leap over the vacancies; there is a certain distance which it
is able to leap over according to its strength; if a number of small
vacancies, though each be very minute, taken together exceed that distance,
it cannot leap over them, and so the shock is prevented.

26. From the before mentioned law of electricity, that points, as they are
more or less acute, draw on and throw off the electrical fluid with more or
less power, and at greater or less distances, and in larger or smaller
quantities in the same time, we may see how to account for the situation of
the leaf of gold suspended between two plates, the upper one continually
electrified, the under one in a person's hand standing on the floor. When
the upper plate is electrified, the leaf is attracted and raised towards
it, and would fly to that plate were it not for its own points. The corner
that happens to be uppermost when the leaf is rising, being a sharp point,
from the extream thinness of the gold, draws and receives at a distance a
sufficient quantity of the electrical fluid to give itself an electrical
atmosphere, by which its progress to the upper plate is stopt, and it
begins to be repelled from that plate, and would be driven back to the
under plate, but that its lowest corner is likewise a point, and throws off
or discharges the overplus of the leaf's atmosphere, as fast as the upper
corner draws it on. Were these two points perfectly equal in acuteness, the
leaf would take place exactly in the middle space, for its Weight is a
trifle, compared to the power acting on it: But it is generally nearest the
unelectrified plate, because, when the leaf is offered to the electrified
plate at a distance, the sharpest point is commonly first affected and
raised towards it; so that point, from its greater acuteness, receiving the
fluid faster than its opposite can discharge it at equal distances, it
retires from the electrified plate, and draws nearer to the unelectrified
plate, till it comes to a distance where the discharge can be exactly equal
to the receipt, the latter being lessened, and the former encreased; and
there it remains as long as the globe continues to supply fresh electrical
matter. This will appear plain, when the difference of acuteness in the
corners is made very great. Cut a piece of _Dutch_ gold (which is fittest
for these experiments on account of its greater strength) into the form of
FIG. 10 the upper corner

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