ELECTRIC LIGHTING
The most important step in the electric field, after the dynamo had been
brought to a fairly workable condition, was its utilization to make
light. It was long known prior to the discovery of practical electric
dynamos, that the electric current would produce an intense heat.
Ordinary fuels under certain favorable conditions will produce a
temperature of 4,500 degrees of heat; but by means of the electric arc,
as high as six, eight and ten thousand degrees are available.
The fact that when a conductor, in an electric current, is severed, a
spark will follow the drawing part of the broken ends, led many
scientists to believe, even before the dynamo was in a practical shape,
that electricity, sooner or later, would be employed as the great
lighting agent.
When the dynamo finally reached a stage in development where its
operation could be depended on, and was made reversible, the first
active steps were taken to not only produce, but to maintain an arc
between two electrodes.
It would be difficult and tedious to follow out the first experiments
in detail, and it might, also, be useless, as information, in view of
the present knowledge of the science. A few steps in the course of the
development are, however, necessary to a complete understanding of the
subject.
Reference has been made in a previous chapter to what is called the
_Electric Arc_, produced by slightly separated conductors, across which
the electric current jumps, producing the brilliantly lighted area.
This light is produced by the combustion of the carbon of which the
electrodes are composed. Thus, the illumination is the result of
directly burning a fuel. The current, in passing from one electrode to
the other, through the gap, produces such an intense heat that the fuel
through which the current passes is consumed.
Carbon in a comparatively pure state is difficult to ignite, owing to
its great resistance to heat. At about 7,000 degrees it will fuse, and
pass into a vapor which causes the intense illumination.
The earliest form of electric lighting was by means of the arc, in which
the light is maintained so long as the electrodes were kept a certain
distance apart.
To do this requires delicate mechanism, for the reason that when contact
is made, and the current flows through the two electrodes, which are
connected up directly with the coils of a magnet, the cores, or
armatures, will be magnetized. The result is that the electrode,
connected with the armature of the magnet, is drawn away from the other
electrode, and the arc is formed, between the separated ends.
As the current also passes through a resistance coil, the moment the
ends of the electrodes are separated too great a distance, the
resistance prevents a flow of the normal amount of current, and the
armature is compelled to reduce its pull. The effect is to cause the two
electrodes to again approach each other, and in doing so the arc becomes
brighter.
It will be seen, therefore, that there is a constant fight between the
resistance coil and the magnet, the combined action of the two being
such, that, if properly arranged, and with powers in correct relation to
each other, the light may be maintained without undue flickering. Such
devices are now universally used, and they afford a steady and reliable
means of illumination.
Many improvements are made in this direction, as well as in the
ingredients of the electrodes. A very novel device for assuring a
perfect separation at all times between the electrodes, is by means of a
pair of parallel carbons, held apart by a non-conductor such as clay, or
some mixture of earth, a form of which is shown in Fig. 116.
The drawing shows two electrodes, separated by a non-conducting
material, which is of such a character that it will break down and
crumble away, as the ends of the electrodes burn away.
[Illustration: _Fig. 116. Parallel Carbons._]
This device is admirable where the alternating current is used, because
the current moves back and forth, and the two electrodes are thus burned
away at the same rate of speed.
In the direct or continuous current the movement is in one direction
only, and as a result the positive electrode is eaten away twice as fast
as the negative.
This is the arc form of lamp universally used for lighting large spaces
or areas, such as streets, railway stations, and the like. It is
important also as the means for utilizing searchlight illumination, and
frequently for locomotive headlights.
Arc lights are produced by what is called the _series current_. This
means that the lamps are all connected in a single line. This is
illustrated by reference to Fig. 117, in which A represents the wire
from the dynamo, and B, C the two electrodes, showing the current
passing through from one lamp to the next.
[Illustration: _Fig. 117. Arc-Lighting Circuit._]
A high voltage is necessary in order to cause the current to leap across
the gap made by the separation of the electrodes.
THE INCANDESCENT SYSTEM.--This method is entirely different from the arc
system. It has been stated that certain metals conduct electricity with
greater facility than others, and some have higher resistance than
others. If a certain amount of electricity is forced through some
metals, they will become heated. This is true, also, if metals, which,
ordinarily, will conduct a current freely, are made up into such small
conductors that it is difficult for the current to pass.
[Illustration: _Fig 118. Interrupted Conductor._]
In the arc method high voltage is essential; in the incandescent plan,
current is the important consideration. In the arc, the light is
produced by virtue of the break in the line of the conductor; in the
incandescent, the system is closed at all times.
Supposing we have a wire A, a quarter of an inch in diameter, carrying a
current of, say, 500 amperes, and at any point in the circuit the wire
is made very small, as shown at B, in Fig. 118, it is obvious that the
small wire would not be large enough to carry the current.
The result would be that the small connection B would heat up, and,
finally, be fused. While the large part of the wire would carry 500
amperes, the small wire could not possibly carry more than, say, 10
amperes. Now these little wires are the filaments in an electric bulb,
and originally the attempt was made to have them so connected up that
they could be illuminated by a single wire, as with the arc system above
explained, one following the other as shown in Fig. 117.
[Illustration: _Fig. 119. Incandescent Circuit._]
It was discovered, however, that the addition of each successive lamp,
so wired, would not give light in proportion to the addition, but at
only about one-fourth the illumination, and such a course would,
therefore, make electric lighting enormously expensive.
This knowledge resulted in an entirely new system of wiring up the lamps
in a circuit. This is explained in Fig. 119. In this figure A represents
the dynamo, B, B the brushes, C, D the two line wires, E the lamps, and
F the short-circuiting wires between the two main conductors C, D.
It will be observed that the wires C, D are larger than the cross wires
F. The object is to show that the main wires might carry a very heavy
amperage, while the small cross wires F require only a few amperes.
This is called the _multiple_ circuit, and it is obvious that the entire
amperage produced by the dynamo will not be required to pass through
each lamp, but, on the other hand, each lamp takes only enough necessary
to render the filament incandescent.
This invention at once solved the problem of the incandescent system and
was called the subdivision of the electric light. By this means the cost
was materially reduced, and the wiring up and installation of lights
materially simplified.
But the divisibility of the light did not, by any means, solve the great
problem that has occupied the attention of electricians and
experimenters ever since. The great question was and is to preserve the
little filament which is heated to incandescence, and from which we get
the light.
The effort of the current to pass through the small filament meets with
such a great resistance that the substance is heated up. If it is made
of metal there is a point at which it will fuse, and thus the lamp is
destroyed.
It was found that carbon, properly treated, would heat to a brilliant
white heat without fusing, or melting, so that this material was
employed. But now followed another difficulty. As this intense heat
consumed the particles of carbon, owing to the presence of oxygen, means
were sought to exclude the air.
This was finally accomplished by making a bulb of glass, from which the
air was exhausted, and as such a globe had no air to support combustion,
the filaments were finally made so that they would last a long time
before being finally disintegrated.
The quest now is, and has been, to find some material of a purely
metallic character, which will have a very high fusing point, and which
will, therefore, dispense with the cost of the exhausted bulb. Some
metals, as for instance, osmium, tantalum, thorium, and others, have
been used, and others, also, with great success, so that the march of
improvements is now going forward with rapid strides.
VAPOR LAMPS.--One of the directions in which considerable energy has
been directed in the past, was to produce light from vapors. The Cooper
Hewitt mercury vapor lamp is a tube filled with the vapor of mercury,
and a current is sent through the vapor which produces a greenish
light, and owing to that peculiar color, has not met with much success.
It is merely cited to show that there are other directions than the use
of metallic conductors and filaments which will produce light, and the
day is no doubt close at hand when we may expect some important
developments in the production of light by means of the Hertzian waves.
DIRECTIONS FOR IMPROVEMENTS.--Electricity, however, is not a cheap
method of illumination. The enormous heat developed is largely wasted.
The quest of the inventor is to find a means whereby light can be
produced without the generation of the immense heat necessary.
Man has not yet found a means whereby he can make a heat without
increasing the temperature, as nature does it in the glow worm, or in
the firefly. A certain electric energy will produce both light and heat,
but it is found that much more of this energy is used in the heat than
in the light.
What wonderful possibilities are in store for the inventor who can make
a heatless light! It is a direction for the exercise of ingenuity that
will well repay any efforts.
_Curious Superstitions Concerning Electricity_
Electricity, as exhibited in light, has been the great marvel of all
times. The word electricity itself comes from the thunderbolt of the
ancient God Zeus, which is known to be synonymous with the thunderbolt
and the lightning.
Magnetism, which we know to be only another form of electricity, was not
regarded the same as electricity by the ancients. Iron which had the
property to attract, was first found near the town of Magnesia, in
Lydia, and for that reason was called magnetism.
Later on, a glimmer of the truth seemed to dawn on the early scientists,
when they saw the resemblance between the actions of the amber and the
loadstone, as both attracted particles. And here another curious thing
resulted. Amber will attract particles other than metals. The magnet did
not; and from this imperfect observation and understanding, grew a
belief that electricity, or magnetism would attract all substances, even
human flesh, and many devices were made from magnets, and used as cures
for the gout, and to affect the brain, or to remove pain.
Even as early as 2,500 years before the birth of Christ the Chinese knew
of the properties of the magnet, and also discovered that a bar of the
permanent magnet would arrange itself north and south, like the
mariners' compass. There is no evidence, however, that it was used as a
mariner's compass until centuries afterwards.
But the matter connected with light, as an electrical development, which
interests us, is its manifestations to the ancients in the form of
lightning. The electricity of the earth concentrates itself on the tops
of mountains, or in sharp peaks, and accounts for the magnificent
electrical displays always found in mountainous regions.
Some years ago, a noted scientist, Dr. Siemens, while standing on the
top of the great pyramid of Cheops, in Egypt, during a storm, noted that
an electrical discharge flowed from his hand when extended toward the
heavens. The current manifested itself in such a manner that the hissing
noise was plainly perceptible.
The literature of all ages and of all countries shows that this
manifestation of electrical discharges was noted, and became the subject
of discussions among learned men.
All these displays were regarded as the bolts of an angry God, and
historians give many accounts of instances where, in His anger, He sent
down the lightning to destroy.
Among the Romans Jupiter thus hurled forth his wrath; and among many
ancient people, even down to the time of Charlemagne, any space struck
by lightning was considered sacred, and made consecrated ground.
From this grew the belief that it was sacrilegious to attempt to imitate
the lightning of the sky--that Deity would visit dire punishment on any
man who attempted to produce an electric light. Virgil relates accounts
where certain princes attempted to imitate the lightning, and were
struck by thunderbolts as punishments.
Less than a century ago Benjamin Franklin devised the lightning rod, in
order to prevent lightning from striking objects. The literature of that
day abounds with instances of protests made, on the part of those who
were as superstitions as the people in ancient times, who urged that it
was impious to attempt to ward off Heaven's lightnings. It was argued
that the lightning was one way in which the Creator manifested His
displeasure, and exercised His power to strike the wicked.
When such writers as Pliny will gravely set forth an explanation of the
causes of lightning, as follows in the paragraph below, we can
understand why it inculcated superstitious fears in the people of
ancient times. He says:
"Most men are ignorant of that secret, which, by close observation of
the heavens, deep scholars and principal men of learning have found
out, namely, that they are the fires of the uppermost planets, which,
falling to the earth, are called lightning; but those especially which
are seated in the middle, that is about Jupiter, perhaps because
participating in the excessive cold and moisture from the upper circle
of Saturn, and the immoderate heat of Mars, that is next beneath, by
this means he discharges his superfluity, and therefore it is commonly
said, 'That Jupiter shooteth and darteth lightning.' Therefore, like as
out of a burning piece of wood a coal flieth forth with a crack, even so
from a star is spit out, as it were, and voided forth this celestial
fire, carrying with it presages of future things; so that the heavens
showeth divine operations, even in these parcels and portions which are
rejected and cast away as superfluous."