The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
John Stuart Mill · en
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_.
CHAPTER XXVIII.
586. _Why does lightning sometimes travel through a "zigzag" course?_