Electricity for Boys Part 12

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 pa.s.sing from one electrode to the other, through the gap, produces such an intense heat that the fuel through which the current pa.s.ses 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 pa.s.s 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 pa.s.ses 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 a.s.suring 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.

[Ill.u.s.tration: _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 s.p.a.ces 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 ill.u.s.trated by reference to Fig. 117, in which A represents the wire from the dynamo, and B, C the two electrodes, showing the current pa.s.sing through from one lamp to the next.

[Ill.u.s.tration: _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 pa.s.s.

[Ill.u.s.tration: _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.

[Ill.u.s.tration: _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 pa.s.s 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 pa.s.s 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 gla.s.s, 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 Superst.i.tions 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 G.o.d 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' compa.s.s. There is no evidence, however, that it was used as a mariner's compa.s.s 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 G.o.d, 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 s.p.a.ce 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.