wo cards instead of one,
which, however, must be kept very little distant from one another,
each of the cards, after the explosion, will be found pierced with one
or more holes, and each hole will have burs on both surfaces of each
card. The hole, or holes, are larger or smaller, according as the
card, &c., is more damp or more dry. It is remarkable, that if the
nostrils are presented to it, they will be affected with a sulphurous,
or rather a phosphoric smell, just like that produced by an excited
electric.

If, instead of paper, a very thin plate of glass, resin, sealing-wax,
or the like, be interposed between the knob of the discharging-rod and
the outside coating of the jar, on making the discharge, this will be
broken in several pieces.

_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. The 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.

_Another Electric Orrery._ (See page 92.)

From the prime conductor of an electric machine suspend six concentric
hoops of metal at different distances from each other, in such a
manner as to represent in some measure the proportional distances of
the planets. Under these, and at a distance of about half an inch,
place a metallic plate, and upon this plate, within each