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The Electric Aurora Borealis








Make a Torricellian vacuum[G] in a glass tube, about three feet long,
and hermetically sealed.[H] Let one end of this tube be held in the
hand, and the other applied to the conductor; and immediately the
whole tube will be illuminated from one end; and when taken from the
conductor will continue luminous, without interruption, for a
considerable time, very often about a quarter of an hour. If, after
this, it be drawn through the hand either way, the light will be
uncommonly brilliant, and, without the least interruption, from one
end to the other, even to its whole length. After this operation,
which discharges it in a great measure, it will still flash at
intervals, though it be held only at the extremity, and quite still;
but if it be grasped by the other hand at the same time, in a
different place, strong flashes of light will dart from one end to the
other. This will continue for twenty-four hours, and often longer,
without any fresh excitation. Small and long glass tubes, exhausted of
air, and bent in many irregular crooks and angles, will, when properly
electrified, exhibit a very beautiful representation of vivid flashes
of lightning.

[G] A Torricellian vacuum is made by filling a tube with pure
mercury and then inverting it, in the same manner as in
making a barometer; for as the mercury runs out, all the
space above will be a true vacuum.

[H] A glass is hermetically sealed by holding the end of it
in the flame of a candle, till it begin to melt, and then
twisting it together with a pair of pincers.





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Previous: The Illuminated Cylinder



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