THEORY OF ELECTRICITY.
In the series of chapters on Heat (Vol. II) and in the chapter on
Magnetism the word molecule was frequently used synonymously with atom.
In chemistry a distinction is made, and as we can better explain the
theory, at least, of electricity by keeping this distinction in mind we
will refer to it here.
It has been stated that there are between sixty and seventy elementary
substances. An elementary substance cannot be destroyed as such. It can
be united with other elements and form chemical compounds of almost
endless variety. The smallest particle of an elementary substance is
called in chemistry an atom. The smallest particle of a compound
substance is called a molecule. The atom is the unit of the element, and
the molecule is the unit of the compound as such. It follows, then, that
there are as many different kinds of atoms as there are elements, and as
many different kinds of molecules as there are compounds. If the
elements have a molecular Structure then two or more atoms of the same
kind must combine to make a molecule of an elementary substance. Two
atoms of hydrogen combine with one of oxygen to form one molecule of
water. It cannot exist as water in any smaller quantity. If we subdivide
it, it no longer exists as water, but as the original gases from which
it was compounded.
We have shown in the series on Sound, Heat and Light that they are all
modes of motion. Sound is transmitted in longitudinal waves through air
and other material substance as vibration. Heat is a motion of the
ultimate particles or atoms of matter, and Light is a motion of the
luminiferous ether transmitted in waves that are transverse. Electricity
is also undoubtedly a mode of motion related in a peculiar way to the
atoms of the conductor.
Notice that there is a difference between conduction and radiation. The
former transmits energy by a transference of motion from atom to atom or
molecule to molecule within the body, while the latter does it by a
vibration of the ether outside--as light, radiant heat, and
electromagnetic lines of force.
For the benefit of those persons who have not read Vol. II, where the
nature of ether is discussed somewhat, let us refer to it here, as it
plays an important part in the explanation of electrical phenomena.
Ether is a tenuous and highly elastic substance that fills all
interstellar and interatomic space. It has few of the qualities of
ordinary matter. It is continuous and has no molecular structure. It
offers no perceptible resistance, and the closest-grained substances of
ordinary matter are more open to the ether than a coarse sieve is to the
finest flour. It fills all space, and, like eternity, it has no limits.
Some physicists suppose--and there is much plausibility in the
supposition--that the ether is the one substance out of which all forms
of matter come. That the atoms of matter are vortices or little
whirlpools in the ether; and that rigidity and other qualities of matter
all arise in the ether from different degrees or kinds of motion.
Electricity is not a fluid, or any form of material substance, but a
form of energy. Energy is expressed in different ways, and, while as
energy it is one and the same, we call it by different names--as heat
energy, chemical energy, electrical energy, and so on. They will all do
work, and in that respect are alike. One difficulty in explaining
electrical phenomena is the nomenclature that the science is loaded down
with. All the old names were adopted when electricity was regarded as a
fluid, hence the word "current." It is spoken of as "flowing" when it
does not flow any more than light flows.
If a man wants to write a treatise on electricity--outside of the mere
phenomena and applications--and wants to make a large book of it, he
would better tell what he does not know about it, for in that way he can
make a volume of almost any size. But if he wants to tell what it really
is, and what he really knows it is, a primer will be large enough. This
much we know--that it is one of many expressions of energy.
Chemistry teaches that heat is directly related to the atoms of matter.
Atoms of different substances differ greatly in weight. For instance,
the hydrogen atom is the unit of atomic weight, because it is the
lightest of all of them. Taking the hydrogen atom as the unit, in round
numbers the iron atom weighs as much as 56 atoms of hydrogen, copper a
little over 63, silver 108, gold 197. Heat acts upon matter according to
the number of atoms in a given space, and not as its weight. Knowing the
relative weights of the atoms of the different metals named, it would be
possible to determine by weight the dimensions of different pieces of
metal so that they will contain an equal number of atoms. If we take
pieces of iron, copper, silver and gold, each of such weight as that all
the pieces will contain the same number of atoms, and subject them to
heat till all are raised to the same temperature, it will be found that
they have all absorbed practically the same quantity of heat without
regard to the different weights of matter. It will be observed that the
piece of silver, for instance, will have to weigh nearly twice as much
as the iron in order to contain the same number of atoms, but it will
absorb the same amount of heat as the piece of iron containing the same
number of atoms, if both are raised to the same temperature. In view of
the above fact it seems that heat acts especially upon the atoms of
matter and is a peculiar form of atomic motion. Heat is one kind of
motion of the atoms, while electricity may be another form of motion of
the same. The two motions may be carried on together. The earth has a
compound motion. It revolves upon its axis once in twenty-four hours,
and it also revolves around the sun once each year. So you see that
there are different kinds of motion that may be communicated to the same
body--all producing different results.
The motion of the individual atom as heat may be, and is, as rapid as
light itself when the temperature is sufficiently high, but it does not
travel along a conductor rapidly as the electro-atomic motion will. If
we apply heat to the end of a metal rod it will travel slowly along the
rod. But if we make the rod a conductor of electricity it travels from
atom to atom with a speed nearer that of the light ray through the
ether. Some modern writers have attempted to explain all the phenomena
of electricity as having their origin in a certain play of forces upon
the ether, and there is no doubt but that the ether plays an important
part in all electrical phenomena as a medium through which energy is
transferred; but ether-waves that are set in motion by the electrical
excitation of ordinary matter are no more electricity than the
ether-waves set up by the sun in the cold regions of space are heat.
They become heat only when they strike matter. Heat, _as such_, begins
and ends in matter;--so (I believe) does electricity.
Do not be discouraged with these feeble attempts to explain the theory
of electricity. All I even hope to do is to establish in your minds this
fundamental thought, to wit, that there is really but one Energy, and
that it is always expressed by some form of motion or the ability to
create motion. Motions differ, and hence are called by different names.
If I should set an emery-wheel to revolving and hold a piece of steel
against it the piece of steel would become heated and incandescent
particles would fly off, making a brilliant display of fireworks. The
heat that has been developed is the measure of the mechanical energy
that I have used against the emery-wheel. Now, let us substitute for the
emery-wheel another wheel of the same size made of vulcanized rubber,
glass or resin. I set it to revolving at the same speed, and instead of
the piece of steel, I now hold a silk handkerchief or a catskin against
the wheel with the same force that I did the steel. If now I provide a
Leyden jar and some points to gather up the electricity that will be
produced (instead of the heat generated in the other case), it would be
found that the energy developed in the one case would exactly balance
that of the other, if it were all gathered up and put into work. The
electricity stored in the jar is in a state of strain, like a bent bow,
and will recoil, when it has a chance, with a power commensurate with
the time it has been storing and the amount of energy used in pressing
against the wheel.
If now I connect my two hands, one with the inside and the other with
the outside of the jar, this stored energy will strike me with a force
equal to all the energy I have previously expended in pressing against
the wheel, minus the loss in heat. If I did it for a long enough time
this electrical spring would be wound up to such a tension that the
recoil would destroy life if one put himself in the path of its
discharge. If all the heat in the first case were gathered up and made
to bend a stiff spring, and one should put himself in its way when
released, this mechanical spring would strike with the same power that
the electrical spring did when the Leyden jar was discharged. This
statement assumes that all the energy in the second experiment was
stored as electricity in the jar. You will be able to see from the
above illustration that heat, electrical energy, and mechanical energy
are really the same. Then you ask, how do they differ? Simply in their
phenomena--their outward manifestations.
While there is much that we cannot know about any of the phenomena of
nature, it is a great step in advance if we can establish a close
relationship between them. It helps to free electricity from many
vagaries that exist in the minds of most people regarding it; vagaries
that in ignorant minds amount to superstition. While it possesses
wonderful powers, they give it attributes that it does not possess. Not
long ago a favorite headline of the medical electrician's advertisement
was "Electricity Is Life," and it was a common thing to see
street-venders dealing out this "life" in shocking quantities to the
innocent multitudes--ten cents' worth in as many seconds.
Science divides electricity into two kinds--static and dynamic. Static
comes from a Greek word, meaning to stand, and refers to electricity as
a stationary charge. Dynamic is from the Greek word meaning power, and
refers to electricity in motion. When Franklin made his celebrated kite
experiment, the electricity came down the string, and from the key on
the end of the string he stored it in a Leyden jar. While the
electricity was moving down the string it was dynamic, but as soon as
it was stored in the Leyden jar it became static. Current electricity is
dynamic. A closed telegraphic circuit is charged dynamically, while the
prime conductor of a frictional electric machine is charged statically.
The distinction is arbitrary and in a sense a misnomer. When we rub a
piece of hard rubber with a catskin it is statically charged because the
substances are what are called non-conductors, and the charge cannot be
conducted readily away. All substances are divided into two classes, to
wit, conductors or non-electrics, and non-conductors or electrics, more
commonly called dielectrics. These, however, are relative terms, as no
substance is either a perfect conductor or a perfect non-conductor.
The metals, beginning with silver as the best, are conductors. Ebonite,
paraffine, shellac, etc., are insulators, or very poor conductors. The
best conductors offer some resistance to the passage of the current and
the best insulators conduct to some extent. If we make a comparison of
electric conductors we find that the metals that conduct heat best also
conduct electricity best. This, it seems to me, is a confirmation of the
atomic theory of electricity so far as it means anything. If a good
conductor, as silver, is subjected to intense cold by putting it into
liquid air, its conductivity is greatly increased. It is well known
that heating a conductor ordinarily diminishes its power to conduct
electricity. This shows that, in order that electrical motion of the
atom may have free play, the heat motion must be suppressed.