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 t rough 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.