Electrified Air
Fix two or three pointed needles into the prime conductor of an
electrical machine, and set the glass in motion so as to keep the
prime conductor electrified for several minutes. If now, an
electometer be brought within the air that is contiguous to the prime
conductor, it will exhibit signs of electricity, and this air will
continue electrified for some time, even after the machine has been
removed into another room.
he air, in this case, is electrified
positively; it maybe negatively electrified by fixing the needles in
the negative conductor while insulated, and making a communication
between the prime conductor and the table, by means of a chain or
other conducting substance.
The air of a room may be electrified in another way. Charge a large
jar, and insulate it; then connect two or more sharp-pointed wires or
needles, with the knob of the jar, and connect the outside coating of
the jar with the table. If the jar be charged positively, the air of
the room will soon become positively electrified likewise; but if the
jar be charged negatively, the electricity communicated by it to the
air will also become negative. A charged jar being held in one hand,
and the flame of an insulated candle held in the other being brought
near the knob of the jar, will also produce the same effect.