561. _What is electricity?_
Electricity is a property of _force_ which resides in all matter, and
which constantly seeks to establish an _equilibrium_.
562. _Why is it called electricity?_
Because it first revealed itself to human observation through a
substance called, in the Greek language, _electrum_. This substance is
known to us as _amber_.
563. _In what way did electrum induce attention to this property of
force in matter?_
Thales, a Greek philosopher, observed that, by briskly rubbing
_electrum_, it acquired the property of _attracting_ light particles
of matter, which moved towards the amber, and attached themselves to
its surface, evidently under the influence of a _force_ excited in the
amber.
564. _What is amber?_
It is a _resinous_ substance, hard, bitter, tasteless, and glossy.
It has been variously supposed to be a vegetable gum, a fossil, and
an animal product. It is probably formed by a _species of ant_ that
inhabit pine forests. The bodies of ants are frequently found in its
substance.
[Verse: "He made darkness his secret place: his pavilion round about
him were dark waters and thick clouds of the skies."]
565. _Why does the rubbing of a stick of sealing-wax cause it to
attract small particles of matter?_
Because it excites in the sealing wax that _force_ which was first
observed in the _amber_. Sealing-wax, therefore, is called an
_electric_ (_amber-like_) body.
566. _Why do we hear of the electric fluid?_
Simply because the term _fluid_ is the most convenient that can be
found to express our ideas when speaking of the _phenomena of electric
force_. But of the nature of electricity, except through its observed
_effects_, nothing is known.
567. _What substances are electric?_
All substances in nature, from the _metals_ to the _gases_. But they
differ very widely in their electrical qualities.
568. _What is positive electricity?_
Electricity, when it exists, or is excited, in any body, to an amount
which is _in excess_ of the amount natural to that body, is called
_positive_ (called also _vitreous_).
569. _What is negative electricity?_
Electricity, when it exists, or is excited, in any body, in an amount
which _is less_ than is the amount natural to that body, is called
_negative_ (called also _resinous_).
570. _Why is "positive" electricity called also "vitreous," and
"negative" electricity called also "resinous"?_
Because some philosophers believe that there is but _one electricity_,
but that it is liable to variations of _quantity_ or _state_, which
they distinguish by _positive_ and _negative_; while other philosophers
believe that there are _two electricities_, which they name _vitreous_
and _resinous_, because they may be induced respectively from
_vitreous_ and _resinous_ substances, and they display forces of
attraction and repulsion.
571. _Upon what do the electrical phenomena of nature depend?_
Upon the tendency of _electricity_ to find an _equilibrium_ between
its _positive_ and _negative_ states (assuming there to be but _one_
fluid); or upon the tendency of _vitreous electricity_ to seek out
and combine with _resinous electricity_ (assuming that there are _two_
fluids).
[Verse: "The Lord also thundered in the heavens, and the Highest
gave his voice; hailstones and coals of fire."]
572. _How does the equilibrium of electricity become disturbed?_
By changes in the condition of matter. As electricity resides in
all substances, and is, perhaps, an essential ingredient in their
condition, so every change in the state of matter--whether from
heat to cold, or from cold to heat; from a state of rest to that of
motion; from the solid to the liquid, or the æriform condition, or
_vice versa_; or whether substances combine chemically and produce new
compounds--in every change _the electrical equilibrium is disturbed_;
and, in proportion to the degree of disturbance, is the force exerted
by electricity to resume its balance in the scale of nature.
573. _How does electricity seek to regain equilibrium?_
By passing through substances that are favourable to its diffusion;
therefore they are called _conducting_ or _non-conducting_ bodies,
according as they favour or oppose the transmission of the electrical
current.
574. _What substances are conductors of electricity?_
Metals, charcoal, animal fluids, water, vegetable bodies, animal
bodies, flame, smoke, vapour, &c.
575. _What substances are non-conductors?_
Rust, oils, phosphorous, lime, chalk, caoutchouc, gutta percha,
camphor, marble, porcelain, dry gases and air, feathers, hair, wool,
silk, glass, transparent stones, vitrefactions, wax, amber, &c. These
bodies are also called _insulators_. Some of these substances, as
chalk, feathers, hair, wool, silk, &c., though non-conductors when
_dry_, become conductors when _wetted_.
_Insulating_--preventing from escaping.
576. _Why are amber and wax classed among the non-conductors, when they
have been pointed out as electrics, and used to illustrate electrical
force?_
It is _because_ they are _non-conductors_ that they have displayed,
under excitement, the attractive force shown in respect to the
particles of matter which were drawn towards their substances. If a bar
of _iron_ were excited, instead of a stick of wax, electricity would be
equally developed; but the iron, _being a good conductor_, would pass
the electricity to the hand of the operator as fast as it accumulated,
and the equilibrium would be undisturbed.
[Verse: "Yea, he sent out his arrows, and scattered them; and he
shot out lightnings and discomfited them."--PSALM XVIII.]
577. _What is the effect when electricity, in considerable force, seeks
its equilibrium, but meets with insulating bodies?_
The result is a violent action in which, _intense heat and light_ are
developed, and in the evolution of which _the electric force becomes
expended_.
578. _What is the cause of electric sparks?_
The electric force, passing through a conducting body to find its
_equilibrium_, is checked in its course by an insulator, and emits a
spark.
579. _What produces the electric light?_
Currents of electricity pass towards each other along wires at the ends
of which two charcoal points are placed. As long as the charcoal points
remain in contact, the electric communication is complete, and no light
is emitted, but, when they are drawn apart, intense heat and light are
evolved.
[Illustration: Figs. 17 & 18.--SHOWING THE EFFECT OF THE UNION AND THE
SEPARATION OF THE CHARCOAL POINTS.]
580. _What is the cause of lightning?_
Lightning is the result of _electrical discharges_ from the _clouds_.
581. _What develops electricity in the clouds?_
Evaporations from the surface of the earth; changes of temperature in
the atmospheric vapour; chemical action upon the earth's surface; and
the friction of volumes of air of different densities against each
other.
[Verse: "His lightnings enlightened the world: the earth saw and
trembled."--PSALM XCVII.]
582. _Why do these phenomena produce electricity?_
Because they disturb the equilibrium of the electric force, and produce
_positive_ and _negative_ states of electricity.
583. _When does lightning occur?_
When clouds, charged with the _opposite electricities_ approach, the
forces rush to each other, and combine in a state of equilibrium.
584. _Why does lightning attend this movement of the forces of
electricity?_
Because the atmosphere, being unable to convey the great charges of
electricity as they rush towards each other, _acts as an insulator_,
and lightning is caused by the _violence of the electricity in forcing
its passage_.
585. _Does lightning ever occur when the conducting power is equal to
the force of the electricity?_
No; electricity passes invisibly, noiselessly, and harmlessly, whenever
it finds a sufficient source of _conduction_.