uctor_, or _insulating substance_; the metal a _conductor_.

When a non-conductor or imperfect conductor, provided it be a thin plate
of matter placed upon a conductor, is brought in contact with an excited
electrical body, the surface opposite to that of contact gains the
opposite electricity from that of the excited body, and if the plate be
removed it is found to possess two surfaces in opposite states. If a
conductor be brought into the neighbourhood of an excited body--the air,
which is a non-conductor, being between them--that extremity of the
conductor which is opposite to the excited body gains the opposite
electricity; and the other extremity, if opposite to a body connected
with the ground, gains the same electricity, and the middle point is not
electrical at all. This is known as _induced_ electricity.

The common exhibition of electrical effects is in attractions and
repulsions; but electricity also produces chemical phenomena. If a piece
of zinc and copper in contact with each other at one point be placed in
contact at other points with the same portion of water, the zinc will
corrode, and attract oxygen from the water much more rapidly than if it
had not been in contact with the copper; and if sulphuric acid be added,
globules of inflammable air are given off from the copper, though it is
not dissolved or acted upon.

Chemical phenomena in connection with electrical effects can be shown
even better by combinations in which the electrical effects are
increased by alterations of different metals and fluids--the so-called
_voltaic batteries_. Such are the decomposing powers of such batteries
that not even insoluble compounds are capable of resisting their energy,
for even glass, sulphate of baryta, fluorspar, etc., are slowly acted
upon, and the alkaline, earthy, or acid matter carried to the poles in
the common order.

The most powerful voltaic combinations are formed by substances that act
chemically with most energy upon each other, and such substances as
undergo no chemical changes in the combination exhibit no electrical
powers. Hence it was supposed that the electrical powers of metals were
entirely due to chemical changes; but this is not the case, for contact
produces electricity even when no chemical change can be observed.

_II.--Radiant or Ethereal Matter_

When similar thermometers are placed in different parts of the solar
beam, it is found that different effects are produced in the differ