Electricity for Boys Part 13

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 superst.i.tions 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 superst.i.tious 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 princ.i.p.al 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 partic.i.p.ating 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."

CHAPTER XVII

POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS

It would be difficult to mention any direction in human activity where electricity does not serve as an agent in some form or manner. Man has learned that the Creator gave this great power into the hands of man to use, and not to curse.

When the dynamo was first developed it did not appear possible that it could generate electricity, and then use that electricity in order to turn the dynamo in the opposite direction. It all seems so very natural to us now, that such a thing should practically follow; but man had to learn this.

Let us try to make the statement plain by a few simple ill.u.s.trations. By carefully going over the chapter on the making of the dynamo, it will be evident that the basis of the generation of the current depends on the changing of the direction of the flow of an electric current.

Look at the simple horse-shoe magnet. If two of them are gradually moved toward each other, so that the north pole of one approaches the north pole of the other, there is a sensible attempt for them to push away from each other. If, however, one of them is turned, so that the north pole of one is opposite the south pole of the other, they will draw together.

In this we have the foundation physical action of the dynamo and the motor. When power is applied to an armature, and it moves through a magnetic field, the action is just the same as in the case of the hand drawing the north and the south pole of the two approaching magnets from each other.

The influence of the electrical disturbance produced by that act permeated the entire winding of the field and armature, and extended out on the whole line with which the dynamo was connected. In this way a current was established and transmitted, and with proper wires was sent in the form of circuits and distributed so as to do work.

But an electric current, without suitable mechanism, is of no value. It must have mechanism to use it, as well as to make it. In the case of light, we have explained how the arc and the incandescent lamps utilize it for that purpose.

But now, attempting to get something from it in the way of power, means another piece of mechanism. This is done by the motor, and this motor is simply a converter, or a device for reversing the action of the electricity.

Attention is called to Figs. 120 and 121. Let us a.s.sume that the field magnets A, A are the positives, and the magnets B, B the negatives. The revolving armature has also four magnet coils, two of them, C, C, being positive, and the other two, D, D, negative, each of these magnet coils being so connected up that they will reverse the polarities of the magnets.

[Ill.u.s.tration: _Figs. 120-121._ ACTION OF MAGNETS IN A DYNAMO]

Now in the particular position of the revolving armature, in Fig. 120, the magnets of the armature have just pa.s.sed the respective poles of the field magnets, and the belt E is compelled to turn the armature past the pole pieces by force in the direction of the arrow F. After the armature magnets have gone to the positions in Fig. 121, the positives A try to draw back the negatives D of the armature, and at the same time the negatives B repel the negatives D, because they are of the same polarities.

This repulsion of the negatives A, B continues until the armature poles C, D have slightly pa.s.sed them, when the polarities of the magnets C, D are changed; so that it will be seen, by reference to Fig. 122, that D is now retreating from B, and C is going away from A--that is, being forced away contrary to their natural attractive influences, and in Fig.

123, when the complete cycle is nearly finished, the positives are again approaching each other and the negatives moving together.

[Ill.u.s.tration: _Figs. 122-123._ CYCLE ACTION IN DYNAMO]

In this manner, at every point, the sets of magnets are compelled to move against their magnetic pull. This explains the dynamo.

Now take up the cycle of the motor, and note in Fig. 124 that the negative magnets D of the armature are closely approaching the positive and negative magnets, on one side; and the positive magnets C are nearing the positive and negatives on the other side. The positives A, therefore, attract the negatives D, and the negative B exert a pull on the positives C at the same time. The result is that the armature is caused to revolve, as shown by the dart G, in a direction opposite to the dart in Fig. 120.

[Ill.u.s.tration: _Figs. 124-125._ ACTION OF MAGNETS IN MOTOR]

When the pole pieces of the magnets C, D are about to pa.s.s magnets A, B, as shown in Fig. 125, it is necessary to change the polarities of the armature magnets C, D; so that by reference to Fig. 126, it will be seen that they are now indicated as C-, and D+, respectively, and have moved to a point midway between the poles A, B (as in Fig. 125), where the pull on one side, and the push on the other are again the same, and the last Figure 127 shows the cycle nearly completed.

The shaft of the motor armature is now the element which turns the mechanism which is to be operated. To convert electrical impulses into power, as thus shown, results in great loss. The first step is to take the steam boiler, which is the first stage in that source which is the most common and universal, and by means of fuel, converting water into steam. The second is to use the pressure of this steam to drive an engine; the third is to drive the dynamo which generates the electrical impulse; and the fourth is the conversion from the dynamo into a motor shaft. Loss is met with at each step, and the great problem is to eliminate this waste.

[Ill.u.s.tration: _Figs. 126-127._ POSITIONS OF MAGNETS IN MOTOR]

The great advantage of electrical power is not in utilizing it for consumption at close ranges, but where it is desired to transmit it for long distances. Such ill.u.s.trations may be found in electric railways, and where water power can be obtained as the primal source of energy, the cost is not excessive. It is found, however, that even with the most improved forms of mechanism, in electrical construction, the internal combustion engines are far more economical.

_Transmission of Energy_

One of the great problems has been the transmission of the current to great distances. By using a high voltage it may be sent hundreds of miles, but to use a current of that character in the cars, or shops, or homes, would be exceedingly dangerous.

To meet this requirement transformers have been devised, which will take a current of very high voltage, and deliver a current of low tension, and capable of being used anywhere with the ordinary motors.

THE TRANSFORMER.--This is an electrical device made up of a core or cores of thin sheet metal, around which is wound sets of insulated wires, one set being designed to receive the high voltage, and the other set to put out the low voltage, as described in a former chapter.

These may be made where the original output is a very high voltage, so that they will be stepped down, first from one voltage to a lower, and then from that to the next lower stage. This is called the "Step down"

transformer, and is now used over the entire world, where large voltages are generated.

ELECTRIC FURNACES.--The most important development of electricity in the direction of heat is its use in furnaces. As before stated, an intense heat is capable of being generated by the electric current, so that it becomes the great agent to use for the treatment of refractory material.

In furnaces of this kind the electric arc is the mechanical form used to produce the great heat, the only difference being in the size of the apparatus. The electric furnace is simply an immense form of arc light, capable of taking a high voltage, and such an arc is enclosed within a suitable oven of refractory material, which still further conserves the heat.

WELDING BY ELECTRICITY.--The next step is to use the high heat thus capable of being produced, to fuse metals so that they may be welded together. It is a difficult matter to unite two large pieces of metal by the forging method, because the highest heat is required, owing to their bulk, and in addition immense hammers, weighing tons, must be employed.

Electric welding offers a simple and easy method of accomplis.h.i.+ng the result, and in the doing of which it avoids the oxidizing action of the forging heat. Instead of heating the pieces to be welded in a forge, as is now done, the ends to be united are simply brought into contact, and the current is sent through the ends until they are in a soft condition, after which the parts are pressed together and united by the simple merging of the plastic condition in which they are reduced by the high electric heat.

This form of welding makes the most perfect joint, and requires no hammering, as the ma.s.s of the metal flows from one part or end to the other; the unity is a perfect one, and the advantage is that the metals can be kept in a semi-fluid state for a considerable time, thus a.s.suring a perfect admixture of the two parts.

With the ordinary form of welding it is necessary to drive the heated parts together without any delay, and at the least cooling must be reheated, or the joint will not be perfect.

The smallest kinds of electric heating apparatus are now being made, so that small articles, sheet metal, small rods, and like parts can be united with the greatest facility.

CHAPTER XVIII

X-RAY, RADIUM, AND THE LIKE

The camera sees things invisible to the human eye. Its most effective work is done with beams which are beyond human perception. The photographer uses the _Actinic_ rays. Ordinary light is composed of the seven primary colors, of which the lowest in the scale is the red, and the highest to violet.

Those below the red are called the Infra-red, and they are the Hertzian waves, or those used in wireless telegraphy. Those above the violet are called Ultra-violet, and these are employed for X-ray work. The former are produced by the high tension electric apparatus, which we have described in the chapter relating to wireless telegraphy; and the latter, called also the Roentgen rays, are generated by the Crookes'

Tube.

This is a tube from which all the atmosphere has been extracted so that it is a practical vacuum. Within this are placed electrodes so as to divert the action of the electrical discharge in a particular direction, and this light, when discharged, is of such a peculiar character that its discovery made a sensation in the scientific world.

The reason for this great wonder was not in the fact that it projected a light, but because of its character. Ordinary light, as we see it with the eye, is capable of being reflected, as when we look into a mirror at an angle. The X-ray will not reflect, but instead, pa.s.s directly through the gla.s.s.

Then, ordinary light is capable of refraction. This is shown by a ray of light bending as it pa.s.ses through a gla.s.s of water, which is noticed when the light is at an angle to the surface.