There are still other definitions or divisions which are in every-day
use, such as “vitreous” electricity, “atmospheric” electricity,
“resinous” electricity, etc.
_Static Electricity._—This is a term employed to define electricity
produced by friction. It is properly employed in the sense of a static
charge which shows itself by the attraction or repulsion between
charged bodies. When static electricity is discharged, it causes more
or less of a current, which shows itself by the passage of sparks or a
brush discharge; by a peculiar prickling sensation; by an unusual smell
due to its chemical effects; by heating the air or other substances in
its path; and sometimes in other ways.
_Current Electricity._—This may be defined as the quantity of
electricity which passes through a conductor in a given time—or,
electricity in the act of being discharged, or electricity in motion.
An electric current manifests itself by heating the wire or conductor,
by causing a magnetic field around the conductor and by causing
chemical changes in a liquid through which it may pass.
NOTE.—_Statics_ is that branch of mechanics which treats of the
forces which keep bodies at rest or in equilibrium. _Dynamics_ treats
of bodies in motion. Hence static electricity is electricity at rest.
The earth’s great store of electricity is at rest or in equilibrium.
_Radiated electricity_ is electricity in vibration. Where the current
oscillates or vibrates back and forth with extreme rapidity, it takes
the form of waves which are similar to waves of light.
_Positive Electricity._—This term expresses the condition of the point
of an electrified body having the higher energy from which it flows to
a lower level. The sign which denotes this phase of electric excitement
is +; all electricity is either positive or,-, negative.
_Negative Electricity._—This is the reverse condition to the above and
is expressed by the sign or symbol-. These two terms are used in the
same sense as _hot_ and _cold_.
_Atmospheric electricity_ is the free electricity of the air which is
almost always present in the atmosphere. Its exact cause is unknown.
The phenomena of atmospheric electricity are of two kinds; there are
the well-known manifestations of thunderstorms; and there are the
phenomena of continual slight electrification in the air, best observed
when the weather is fine; the aurora constitutes a third branch of the
subject.
_Dynamic Electricity._—This term is used to define current electricity
to distinguish it from static electricity. This is the electricity
produced by the dynamo.
_Frictional electricity_ is that produced by the friction of one
substance against another.
_Resinous Electricity._—This is a term formerly used, in place of
negative electricity. The phrase originated in the well known fact that
a certain (negative) kind of electricity was produced by rubbing rosin.
_Vitreous electricity_ is a term, formerly used, to describe that kind
of electricity (positive) produced by rubbing glass.
_Magneto-electricity_ is electricity in the form of currents flowing
along wires; it is electricity derived from the motion of magnets—hence
the name.
_Voltaic Electricity._—This is electricity produced by the action of
the voltaic cell or battery.
_Electricity itself is the same thing, or phase of energy, by whatever
source it is produced_, and the foregoing definitions are given only as
a matter of convenience.