inches in length, with three large cells of a
bichromate battery.

Mr. Spottiswood of London has just had completed for him the largest
induction coil ever made. It has two primary coils, one containing
sixty-seven pounds of wire, and the other eighty-four pounds, the wire
being .096 inch in diameter. The secondary coil is two hundred and
eighty miles long, and has 381,850 turns. This coil is made in three
parts, the diameter of the wire in the first part being .0095 inch; of
the second part, .015; and the third part, .011. With five Grove cells
this induction coil has given a spark forty-two inches long, and has
perforated glass three inches thick.

The electricity thus developed in secondary coils is of the same
character as that developed by friction; and all of the experiments
usually performed with the latter may be repeated with the former, many
of them being greatly heightened in beauty and interest. Such, for
instance, are the discharges in vacuo in Geisler tubes, exhibiting
stratifications, fluorescence, phosphorescence, the production of ozone
in great quantity, decomposition of chemical compounds, &c.

The electricity developed by friction upon glass, wax, resin, and other
so-called non-conductors, has heretofore been called static electricity,
for the reason that when it was once originated upon a surface it would
remain upon it for an indefinite time, or until some conducting body
touched it, and thus gave it a way of escape. Thus, a cake of wax if
rubbed with a piece of flannel, or struck with a cat-skin or a fox-tail
becomes highly electrified, and in a dry atmosphere will remain so for
months. Common air has, however, always a notable quantity of moisture
in it; and, as water is a conductor of electricity, such damp air moving
over the electrified surface will carry off very soon all the
electricity.

Again, the electricity developed through chemical action in a battery
and through the inter-action of magnets and coils of wire has been
called dynamic electricity, inasmuch as it never appeared to exist save
when it was in motion in a completed circuit. This, however, is not
true; for if one of the wires from a galvanic battery be connected with
the earth, and the other wire be attached to a delicate electrometer, it
will be found that the latter gives evidence of electrical excitement in
the same manner as it does for the electricity developed by friction in
another body. This is sometimes called _ten