614. _What is thunder?_
Thunder is the _noise which succeeds the rush_ of the electrical fluid
through the air.
615. _Why does noise follow the commotion caused by electricity?_
Because, by the violence of the electric force, vast _fields of air
are divided_; great volumes of air are _rarefied_; and _vapours_ are
_condensed_, and thrown down as _rain_. Thunder is therefore caused by
the _vibrations of the air_, as it collapses, and seeks to restore its
own _equilibrium_.
616. _Why is the thunder-peal sometimes loud and continuous?_
Because the electrical discharge takes place near the hearer, and
therefore the vibrations of the air are heard in their full power.
617. _Why is the thunder-peal sometimes broken and unequal?_
Because the electrical discharge takes place at a _considerable
distance_, and the vibrations are affected in their course by
_mountains_ and _valleys_. Because, also, the _forked arms_ of the
lightning strike out in different directions, causing the sounds of
thunder to reach us from _varying distances_.
[Verse: "Lo, these are parts of his ways; but how little a portion
is heard of him? but the thunder of his power who can understand?"--JOB
XXV.]
618. _Why has the thunder-peal sometimes a low grumbling noise?_
Because the electrical discharges, though violent, take place _far
away_, and the vibrations of the air _become subdued_.
619. _Why does the thunder-peal sometimes follow immediately after the
flash of lightning?_
Because the discharge of electricity takes place near the hearer.
620. _Why does the thunder-peal sometimes occur several seconds after
the flash?_
Because the discharge takes place far away, and _light_ travels with a
much greater velocity than _sound_.
621. _Through what distance will the sound of thunder travel?_
Some _twenty or thirty miles_, according to the _direction of the
wind_, and the violence of the peal.
622. _Through what distance will the light of lightning travel?_
The _light_ of lightning, and its reflections, will penetrate through a
distance of from _a hundred and fifty to two hundred miles_.
623. _How may we calculate the distance at which the electric discharge
takes place?_
Sound travels at the rate of _a quarter of a mile in a second_. If,
therefore, the peal of thunder is heard _four seconds_ after the flash
of lightning, the discharge took place about a mile off. The pulse
of an adult person beats about _once in a second_; therefore, guided
by the pulse, any person may calculate the probable distance of the
storm:--
2 beats, 1/2 a mile.
3 beats, 3/4 of a mile.
4 beats, 1 mile.
5 beats, 1-1/4 miles.
6 beats, 1-1/2 miles.
7 beats, 1-3/4 miles.
8 beats, 2 miles, &c.
Attention should be paid to the _direction and speed of the wind_, and
some modifications of the calculation be made accordingly. Persons
between 20 and 40 years of age should count _five beats of the pulse to
a mile_; under 20, _six beats_.
[Verse: "The clouds poured out water; the skies sent out a sound;
thine arrows also went abroad."]
624. _Why are electric storms more frequent in hot than in cold
weather?_
Because of the _greater evaporation_, as the effect of heat; and also
of the _effect of heat_ upon the particles of all bodies.
625. _Why do electric storms frequently occur after a duration of dry
weather?_
Because _dry air_, being a bad conductor, prevents the _opposite
electricities_ from finding their _equilibrium_.
626. _Why is a flash of lightning generally succeeded by heavy rain?_
Because the electrical discharge destroys the _vescicles_ of the
vapours. If a number of _small soap-bubbles_ floating in the air were
_suddenly broken_ by a violent commotion of the atmosphere, the _thin
films_ of the bubbles would form _drops of water_, and fall _like rain_.
627. _Why is an electrical discharge usually followed by a gust of
wind?_
Because the equilibrium of the atmosphere is disturbed by the _heat
and velocity of lightning_, and the _condensation of vapour_. Air,
therefore, rushes towards those parts where a degree of _vacuity_ or
_rarefaction_ has been produced.
628. _What is a thunderbolt?_
The name _thunderbolt_ is applied to an electrical discharge, when the
lightning appears to be developed with the greatest intensity around a
nucleus, or centre, as though it contained a burning body. But there
is, in reality, _no such thing as a thunderbolt_.
[Verse: "The voice of the Lord is upon the waters: the God of glory
thundereth; the Lord is upon many waters."--PSALM XXIX.]
629. _Why do electric storms purify the air?_
Because they restore the _equilibrium of electricity_ which is
essential to the salubrity of the atmosphere; they intermix the _gases
of the atmosphere_, by agitation; they _precipitate the vapours_
of the atmosphere, and with the precipitation of vapours, _noxious
exhalations_ are taken to the earth, where they become absorbed; they
also contribute largely to the formation of _ozone_, which imparts to
the air corrective and restorative properties.
630. _What is ozone?_
Ozone is an _atmospheric element_ recently discovered, and respecting
which differences of opinion prevail. It is generally supposed to be
_oxygen_ in a state _of great strength_, constituting a variety of form
or condition.
631. _Why do we know that electricity contributes to the formation of
ozone?_
Because careful observations have established the fact that the
proportion of _ozone_ in the atmosphere is _relative to the amount of
electricity_.
632. _What are the properties of ozone?_
It displays an extraordinary power in the neutralisation of
putrefactions, rapidly and thoroughly counteracting noxious
exhalations; it is the most powerful of all _disinfectants_.
Schonbien, the discoverer of _ozone_, inclines to the opinion
that it is a _new chemical element_. Whatever it may be, there
can be no doubt that it plays an important part in the economy of
nature. Its _absence_ has been marked by pestilential ravages, as
in the _cholera_ visitations; and to its _excess_ are attributed
epidemics, such as _influenza_. It was found, during the last
visitation of cholera, that the _fumigation of houses with
sulphur_ had a remarkable efficacy in preventing the spread of
the contagion. The combustion of sulphur ozonised the atmosphere;
the same result occurs through the emission of _phosphoric
vapours_; ozone is also developed by the electricity evolved by
the _electrical machine_, and in the greater _electrical phenomena
of nature_. The smell imparted to the air during an electric
storm is identical with that which occurs in the vicinity of an
electrical apparatus--it is a _fresh_ and _sulphurous_ odour. The
opinion is gaining ground that the respiration of animals and the
combustion of matter are sources of ozone, and that plants produce
it when under the influence of the direct rays of the sun. It is
also believed to be produced by water, when the sun's rays fall
upon it. The most recent opinion respecting ozone is, that it is
_electrized oxygen_. The subject is of vast importance, and opens
another field of discovery to the pioneers of scientific truth.
[Verse: "The voice of thy thunder was in the heaven: the lightnings
lightened the world, the earth trembled and shook."--PSALM LXVII.]
633. _What is magnetism?_
_Magnetism_ is _the electricity of the earth_, and is characterised by
the circulation of _currents of electricity passing through the earth's
surface_.
634. _What are magnetic bodies?_
Magnetic bodies are those that exhibit phenomena which show that
they are under the influence of _terrestrial electricity_, and which
indicate the direction of the _poles_, or _extreme points_, _of
magnetic force_.
635. _What is Galvanism?_
Galvanism is the action of _electricity upon animal bodies_, and is so
called from the name of its first discoverer, Galvani.
636. _What is Voltaic electricity?_
Voltaic electricity is the electricity that is developed during
_chemical changes_, and is so called after Volta, who enlarged upon the
theory of Galvani.
637. _What are the differences between mechanical, or frictional
electricity, Voltaic electricity, Galvanism, and magnetism?_
_Frictional_ electricity is electricity _suddenly_ liberated under the
effects of the _motion_, or the mechanical disturbance of bodies.
_Voltaic_ electricity is a _steady flow_ of an electric current,
arising from the _gradual changes_ of _chemical_ phenomena.
_Galvanism_ and _Voltaism_ are almost _identical_, since the latter
is founded upon, and is a development of, the former. But the term
_Galvanism_ is frequently used when speaking of the development of
electricity in _animal bodies_.
_Magnetism_ is the electricity of the _earth_, and is understood to
imply the _fixed electricity of terrestrial bodies_.
[Verse: "And I heard as it were the voice of a great multitude, and
as the voice of many waters, and as the voice of mighty thunderings,
saying Alleluia: for the Lord God omnipotent reigneth."--REV. XIX.]
Man knows not _what electricity is_; yet, by an attentive
observance of its _effects_, he avails himself of the power
existing in an unknown source, and produces marvellous results.
When the Grecian philosopher, Thales, sat rubbing a piece of
amber, and watching the attraction of small particles of matter
to its surface, he little knew of the mighty power that was then
whispering to him its offer to serve mankind. And when Franklin,
with the aid of a boy's plaything, drew down an electric current
from the clouds, and caught a spark upon the knuckles of his hand,
_even he_ little conjectured that the time was so near when that
strange element, which sent its messenger to him along the string
of a kite, would become one of man's most submissive servants.
So many great results have sprung from the careful observation
of the simplest phenomena, that we should never pass over
inattentively the most trifling thing that offers itself to our
examination. Nature, in her revelations, never seeks to _startle_
mankind. The formation of a rock, and the elaboration of a truth,
are alike the work of ages. It was the simple blackening of silver
by the sun's rays which led to the discovery of the _chemical
agency of light_. It was the falling of an apple which pointed
Newton to the discovery of the _laws of gravitation_. It was the
force of steam, observed as it issued from beneath the lid of a
kettle, that led to the invention of the _steam-engine_. And it is
said of Jacquard, that he _invented the loom_ which so materially
aided the commerce of nations, while watching the motions of his
_wife's fingers_, as she plied her knitting. As great discoveries
spring from such small beginnings, who among us may not be the
herald of some great truth--the founder of some world-wide
benefaction?
That the area of discovery has not perceptibly narrowed its
limits, is evident from the fact that the greatest elements in
nature are still mysteries to man. And though it may not be within
the power of a finite being to unravel the chain of wonders that
enfold the works of an infinite God,--still it is evident, from
the progress which discovery has made, and from the good which
discovery has done, that God _does_ invite and encourage the human
mind to contemplate the workings of Divine power, and to pursue
its manifestations in every element, and in every direction.
The wonderful force of _electricity_ astonishes us all the more
when we view it in contrast with that equally wonderful element,
_light_. We have seen that light travels with a velocity of
192,000 miles in a second, but that it falls upon a delicate
balance so gently, that it produces no perceptible effect. As far
as we know the nature of _electricity_, it is even _more ethereal_
than _light_; yet, while the _ether of light_ falls harmlessly and
imperceptibly--even with the momentum of a flight of _ninety-five
millions of miles_, the _ether of electricity_, bursting from
a cloud only _five hundred yards_ distant, will split massive
stones, level tall towers with the dust, strike majestic trees
to the ground, and instantly extinguish the life of man! _Why_
does _the one ether_ come divested of all mechanical force, while
that which seems to be _even more ethereal_ than it, is capable
of exerting the mightiest force over material things? Does it not
appear that the Creator of the universe has established these
paradoxes of power to testify his Omnipotence--to show to man that
with Him all things are possible; and that, in the grand cosmicism
of the universe, every attribute of Omnipotence has been fulfilled?
[Verse: "And the seventh angel poured out his vial into the air; and
there came a great voice out of the temple of heaven, from the throne,
saying, It is done."--REV. XVI.]
Let us now consider man's relation to this Omnipotence. He sees
that electricity smites the tall edifice, and observes that in
doing so it displays a choice of a certain substance through
which it passes harmlessly, and that its violence is manifested
only when its path is interrupted. Man, taking advantage of this
preference of electricity for a particular conductor, stretches
out an arm of that substance, and points it upwards to the
clouds; electricity accepts the invitation, and passes harmlessly
to the earth. But this not all: man learns by observation that
electricity resides in all matter; that it may be collected or
dispersed; that it travels along a good conductor at the rate
of _half-a-million of miles in a second of time_; he constructs
a battery, a kind of scientific fortress, in which he encamps
the great warrior of nature; and then, laying down a conducting
wire, he liberates the mighty force: but its flight must be on
the path which man has defined, and its journey must cease at the
terminus which man has decreed, where, by a simple contrivance of
his ingenuity (the movements of a magnetic needle), the electric
current is made to deliver whatever message of importance he
desires to convey. Thus, the element which in an instant might
deprive man of life, is subdued by him, and made the obedient
messenger of his will.