Electricity explained

Chapter I. Detecting Electricity With A Telephone Receiver

WE do not know what electricity is any more than we know what is lightning. Many theories have been advanced as to what men think this peculiar force is, but as yet we cannot say that we can define it. And yet we can see it and hear it. And we also can hear lightning. You say we can hear only the explosive discharge of lightning. Yes; but we can hear lightning itself, the moment it flashes, even though it is far from us. How? Simply by connecting a telephone receiver between the gas pipe and the water pipe in the house. Or if you live in the country where there is no gas pipe, put one post of a telephone receiver in connection with the drainage pipe in the kitchen and connect the other post of the receiver with the ground by means of a water pipe, or the kitchen pump.

Whenever you see lightning flashes, foretelling an approaching electric storm, put the receiver to your ear and listen, and you will hear the lightning bizz-zz as it discharges. This is static electricity discharging in the atmosphere. Now static electricity is electricity at rest, which, when disturbed, discharges with considerable force. And force, as an electrical term, means volts. The atmosphere is full of this static electricity, and when it becomes heavy with it, or, in other words, when the atmosphere is fully charged with electricity, it breaks loose in severe discharges, which often prove fatal to destructible things within its path.

There is not so much of this static electricity in the atmosphere in winter as in summer, but there is a great deal of it in the earth, and we can feel it and see it and hear it on the coldest day by walking briskly over a heavy carpet, and stopping quickly by a gas pipe or other grounded pipe, and placing our finger or hand near the pipe. A spark will fly from the hand to the metal pipe, and the positive electricity which we have picked up and stored temporarily in our body will jump back to earth, which is always negatively charged, with force (voltage) enough to produce a spark. And it takes twenty thousand volts to jump across space. Thus we see that there is surrounding us a power capable of producing great force. And yet we cannot harness it because it is instantaneous. With a single flash hundreds of thousands of volts are discharged between the clouds and the earth, and are lost. The average voltage in a flash of lightning is calculated to be about fifty million volts.

Many interesting experiments can be made with our telephone receiver. In ordinary weather, when we listen to it, as it is connected between two grounded pipes, we can hear very feebly a singing sound as of machinery. It is induction from the dynamo electricity which feeds the town. The secondary winding of an alternating-current transformer is generally grounded, and if the town is equipped with trolley cars we will hear through our receivers a singing noise, sometimes loud and sometimes faint, as more or less cars take up the power into their motors.

If we put a box-kite up in the air, with thin bare copper wire wound around the frame, or run an insulated copper wire up the side of a house and connect it with a number of bare copper wires hung from

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the top of a flagpole, so as to catch the electric waves, and connect the end of this aerial with a very sensitive telephone receiver, and have this receiver also connected to the ground, we will hear wireless telegraph stations communicating with each other; and if we learn the Morse code and the Wireless Continental Telegraph code we may be able to read their messages.

In order to catch distant messages from the air, however, the aerial must reach five hundred feet above sea level, unless we employ a wireless detector with our receiver, the construction and use of which we will learn in another chapter. Also we must employ a tuning coil to cut out more than one message at a time. Without a tuning system (which will be described later) we would hear the dots and dashes of several messages at the same time, and we could not translate them into words.

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WIRELESS CONTINENTAL TELEGRAPH CODE.

A lightning-rod on a country house will serve the purpose of an aerial if cut off from the ground and a wireless detector inserted between the two severed ends. But it must be well insulated from the house, as all lightning-rods should be, or the electric waves will jump to earth without going through the receiver. Electricity always takes the shortest path it can find to travel on, and this is most peculiar about a jumping spark.

Now let us see what a telephone receiver is, and how it is made. When Alexander Graham Bell first invented the telephone, in the spring of 1876, he had a coil of wire wound around an iron core. He placed two of these coils at a distance, connecting one end of each coil together and the other free ends he connected with a battery, one to the negative pole and the other to the positive. In front of each of these magnets was placed a tin plate, close to the magnet cores, but not touching them, and when Mr. Bell tapped on one of these plates, so that it pressed against the magnet core, the battery current was modulated and the distant magnet core would attract its tin plate. And when he talked loudly in front of one of these tin diaphragms, the sound waves pushed it varyingly toward the magnet, and accordingly the distant magnet pulled toward itself its tin diaphragm. And when these magnets were each inclosed in a case of rubber the action was intensified. So upon this principle the telephone receiver was made.

When we unscrew the cap of the receiver which we use we find that the tin diaphragm sticks to the magnets, even when there is no battery connected with the magnet winding. Mr. Bell found that when the magnet cores were made of steel, permanently magnetized, his telephones worked more successfully than with soft iron cores, and that one receiver could be directly connected to the other without any electric current in the circuit, and when he talked into one, the distant diaphragm would vibrate accordingly. Thus he gave us the first telephone.

In another chapter we will learn about these lines of force which are invisible but which encircle all magnets, extending out beyond the end. And since these lines of force do extend beyond the ends of magnets we can see how that, when a diaphragm vibrates in front of a permanent magnet core, it disturbs these lines of force and changes their direction. This induces a varying current of electricity in the magnet of which the steel core forms a part, and this varying current, as it circulates around the distant magnet, increases and decreases the magnetism of the distant steel core, and the diaphragm which is in front of this permanently magnetized core vibrates in unison with the other transmitting diaphragm. So if we take two telephone receivers and connect them together with two wires we will have a complete telephone line, providing our receiver magnets are permanently magnetized. Because of the loss of current in the connecting wires, however, and the stiffness of the receiver diaphragms, this is not a practical way to telephone over a distance exceeding two hundred feet.

Now about the magnets in the telephone receiver to which we found the diaphragm sticking. Most receivers have two magnets connected like the two magnets in an electric bell — in series. Such receivers are bipolar. The cores of these magnets appear to be permanently magnetized, but they are soft iron cores and we know that only steel can be permanently magnetized. Then they must be connected with steel magnets, and upon examination we find in our receiver a horseshoe steel magnet the north-poled end of which connects with one magnet core and the south-poled end of which connects with the other magnet core.

Thus we see that the quickest varying currents of electricity, positive and negative, will vibrate the diaphragm of a telephone receiver, and if we connect each post to separate ground connections, the slightest disturbed current may be heard as it surges back and forth through the earth.

Chapter II. Invisible Lines Of Force

Every one knows what a horseshoe magnet is, but not every one knows that one of the greatest principles of applied electricity lies in the construction of such a magnet. Without a permanent magnet in the form of a steel needle, the ships of the sea would not venture to sail beyond the horizon, for there is a drawing magnetism of the earth, the composition of which has not yet been discovered, near the North Pole, which attracts this needle of the mariner's compass. When we look at the markings of a compass and see the needle pointing to the letter N, we should not conclude that this is the north pole of the magnetic needle. The end which rests over the letter S is the north-poled end, because like poles of a magnet repel each other, and unlike poles attract one another. And if the earth's North Pole attracts the end at letter N, then this end of the needle must be of south polarity.

A piece of iron is composed of molecules of iron ore, welded together in a mass, which when heated in a furnace will expand. The red-hot horseshoe that a blacksmith is hammering looks very much thicker when he takes it out of the furnace than it does when he has finished hammering it. And it is made steel by crowding these molecules together. So we see that even while in a solid mass these molecules can be made to change their shape.

If we wind a coil of wire, insulated by a covering, around a bar of soft iron and pass a battery current of electricity through this wire, we will make a magnet of the iron bar which will attract iron. But the moment we disconnect the battery current the bar of iron is no longer a magnet. Why? In passing an electric current through the wire wound around the iron we forced the molecules to take definite shape in the iron bar. But in soft iron they fall back again into irregular shapes when the current is cut off. If we try the same experiment with a bar of steel, when we break the electric circuit, and take the coil of wire off the bar we still find it has the properties of magnetism, and will attract iron substances smaller and lighter than itself. The fact is that the molecules have been so crowded together that there is no room for them to fly back into irregular shapes after they have been magnetized. Steel is not elastic like soft iron, and will break before it will bend. It is true that the molecules do try to fall back irreguarly, and succeed in so doing after some years. That is why permanent magnets sometimes have to be remagnetized. Now to understand how these molecules act we may resort to a simple experiment.

If we sprinkle some iron filings on a paper and underneath this hold a bar of steel, permanently magnetized, we will see the filings try to arrange themselves in form. And by tapping the edge of the paper, to aid the iron dust in jumping about, if the magnet io ELECTRICITY EXPLAINED

is held lengthwise underneath, the form will become definitely symmetrical, arranging as shown by the dotted lines in Figure I. These regular lines, which we trace in the iron dust, bulge out from the center and stretch from one pole of the magnet to the other, remaining thickest around the two ends. These represent our invisible lines of force. And while there is magnetism in any metal capable of retaining it, there will be these invisible lines of force surrounding that metal. One end of the magnet will be the north pole and the other end will be the south pole. And if the magnet is bent in the shape of a horseshoe, the lines of force will be strongest between the two ends.

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FIGURE I.

If we have a very powerful horseshoe magnet we will find it difficult to pass a plate of copper between the two poles, which plate would cut these lines of force. And with such a magnet we could blow out an electric arc light or any electric draw spark,

ELECTRICITY EXPLAINED n

which would break sooner than cut the lines of force. By snapping two live electric wires together between the two poles of such a magnet draw sparks will go out with an explosive report. The armature of a generator cuts these lines of force and produces a current of electricity in the armature coils in so doing. We shall learn of this later, but before we leave this subject we must know how to determine which is the north pole, and which is the south pole of an electric current.

When we pass a direct current of electricity through a coil of insulated wire wrapped around a bar of iron we must have a positive flow of current and a negative. The positive flow will magnetize one end of the bar, the center will be neutral, and the outflowing negative current will magnetize the other end. And if we hold a compass needle near the magnet, the end of the coil receiving the positive current will draw toward itself that point of the needle which rests over the letter N. Therefore, since unlike poles attract each other, and since the point of the needle resting over N is of south polarity, the end of a coil of wire receiving the positive flow of current must be the north pole and the end around which the negative current flows out must be the south pole.

Now, when we know that electric current deflects a compass needle it is very easy to understand how meters are made to measure the current. Take a good compass and wrap around its diameter, from letter N to letter S, a few turns of fine wire. Pass a battery current through this and the needle jumps at right angles to the wires. Insert a slight resistance in the circuit, and the needle will jump in a direction less than a right angle. And insert a high resistance in the circuit and the compass needle will hardly move. With a disc chart for the face of the compass we can thus measure any resistance.

Chapter III. Kinds Of Currents Produced By Electricity

There are five distinct kinds of currents which electricity can be made to produce — the direct current, the alternating current, the pulsating current, the oscillating current, and the undulating current. And it is interesting to follow the history of this science of electricity, and see how these currents were developed by experimental philosophers.

The first principles of electricity were noticed in the metal called loadstone — earth's natural magnet. Then it was found by ancient experimenters that amber — a fossil gum found in certain geological formations — when rubbed by the skin of a cat or a piece of flannel, became magnetized, and was capable of attracting light bodies, such as pieces of silk and paper and feathers. This all happened six hundred years before the Christian era. The Greek word for amber is elektron, and from this word the term electricity was derived.

About the middle of the seventeenth century a German philosopher, Otto Von Guericke, invented an electric machine. He had found that glass could be made magnetic by friction as well as amber. By his machine he automatically rubbed a piece of revolving glass and then drew sparks from it with his hands. This gave static discharges, which oscillated to and from separate posts on the machine when the glass was revolved. And to-day we call such a current an oscillating current. This electric machine was improved upon by an Italian experimenter, Aloisio Galvani, who one day, while using it, caused some sparks to jump to a frog's leg, and when he did so he noticed the muscles contracted with every spark. After this he found that without the aid of any electricity from his machine, when he placed two dissimilar pieces of metal at a distance on the muscle of a frog's leg, just such convulsions occurred.

This experiment was followed by Alessandro Comte Volta, an Italian philosopher, who found that by placing a piece of zinc on one part of an animal's flesh and a piece of silver on a distant part of the animal, and connecting the two by a metallic arc, the muscles of the animal would contract and stay so until the half ring of metal was taken away. It was then clear that when two such pieces of metal were laid on a wet surface a slight electric current would be produced.

This was successfully tried by placing the zinc and the silver near together in a jar of salt water. Here then was another current, the direct current. And to this day the direct current is mostly produced chemically. For this reason it is one of the most expensive currents produced, and is not used where other currents will do the work. But there are cases where necessity demands it. For instance, the telegraph and also the telephone are dependent upon the direct current. With an alternating current the telegraph relay would rattle like a loud buzzer every time the distant operator depressed his transmitting key in sending messages. And if we were to talk over the telephone wires with an alternating current, our voices would quiver.

But it is well to note right here that at the telephone central offices there are two and sometimes three currents used — the direct current to talk with, and the alternating current, or for party wires the pulsating current, for central to ring the subscriber's bell. This is because the most serviceable bell for telephone signaling is the polarized bell which is used in connection with a condenser. In another chapter we will learn of what material condenser is made and to what use it is put.

The alternating current already mentioned is produced by machinery. From the word we know that this current must alternate, going backward and forward, as it does^ This is the cheapest commercial electric current produced, and by the aid of step-down or step-up transformers can be carried a great distance and increased or decreased in voltage at will. Alternating current is measured by its voltage. There is not much amperage to it. When the alternations are very rapid it will heat carbon filaments in incandescent lamps, and all other high resistances while hot. When used with a condenser in circuit the alternating current will surge back and forth through any high resistance, such as a telephone bell, which has a resistance of one thousand ohms, and without heating will pull and release the armature alternately, causing the hammer to strike both bell gongs.

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If we take a horseshoe permanent magnet and revolve between its ends a coil of wire we will produce in this coil, noticeable at its two free ends, an alternating wave every time the coil is revolved. There are invisible lines of force between the two ends, or north and south poles of the permanent magnet, and as the coil of wire is revolved between these poles, it keeps cutting these lines of force. The alternating wave is always represented as in Figure II. And when half such an alternating wave is collected from a specially constructed dynamo, we get another current — the pulsating current. We shall learn more about this current later, which is used to peculiar advantage in the party-line telephone system of selective ringing.

FIGURE II.

A current very much like the pulsating current, but which requires no dynamo to produce it, is called the undulating current. If we connect an electric bell or buzzer with two or three battery cells and then place a finger of one of our hands on the iron frame and another finger on the adjustable contact screw, we will get a shock. The current we thus get is an undulating current. It feels like an alternating current, but it differs from that in its manner of production and in its varying strength. It is not as constant as an alternating current, and requires a close adjustment of the bell armature to keep it from varying. But it has recently been found that by including powerful inductive magnets wound with heavy wire, in circuit between the battery cells and the buzzer, the voltage can be greatly increased, so that a few dry cells battery and a small electric buzzer connected with a large inductive coil of wire in circuit will give an undulating current between the frame of the buzzer and the adjustable contact screw powerful enough to light several incandescent lamps. This is a simple experiment which any one can make, and from which much can be learned.

Having a buzzer equipped with an adjusting spring to loosen or tighten the armature we can increase or decrease this current at will, thus doing away with a rheostat or any other costly means of control. Then, too, if we connect a telephone receiver between the contact screw and the frame of the buzzer, and hold our receiver in a jar or glass tumbler, we will produce a musical note. Thus we can understand how the telharmonium produces electrical music, only that, instead of using an undulating current, Dr. Cahill, its inventor, makes use of the alternating current. There are one hundred and forty-eight dynamos running in the Telharmonic Hall in New York City, all at different speed, and with a keyboard composed of electrical switches. The current is controlled and sent out over two wires terminating in a telephone receiver.

Another interesting experiment we can try with our receiver and buzzer is to place the hand tightly over the cap of the telephone receiver, and quickly releasing it as quickly again clap the hand over the cap. With practice we can make our receiver talk like a child when it first attempts to say "papa" and "mamma/' With a suitable set of mouths capable of being opened and closed at will, to produce different vowel sounds and words, we could make a very good electrically talking machine. But the cost would far exceed that of the phonograph, which does more perfect work than an undulating current would do.

FIGURE III.

We have given some attention to the oscillating current, and found it was first produced by an electric machine. .But it is more easily and much more cheaply produced by the induction coil. An oscillating wave is shown in Figure III, and is one which dies away in space, thus differing from an alternating current wave.

Electro-magnetic induction was the result of Michael Farady's experiments. Farady, an English scientist, found that when he inserted a steel rod, permanently magnetized, in a coil of wire the two ends of which were connected to an electroscope, a current of electricity was produced in the coil, and by quickly moving the permanent magnet to and fro in the coil intermittent currents were produced. Then he substituted a coil of heavy wire wound on a soft iron bar and connecting with a battery, in place of the permanent magnet, and found that by inserting this in the coil of wire these intermittent currents were intensified. Afterward he wound the second coil over the heavy wire coil and passed the positive current through this primary coil to an armature made of iron and held away from the core by a spring, and through a contact screw against which this armature rested, to the negative side of the battery current. When the circuit was thus closed the current flowing through the magnet would draw the iron armature to its core and away from the contact screw, so breaking the circuit and demagnetizing the core, allowing the spring to pull back the armature against the contact screw again, thus closing the circuit and repeating the operation. This produced intermittent currents in the secondary coil, which contracted the muscles when the two ends of this coil were held in the hand, and was called the faradic current, after its inventor.

But later it was found that when the secondary coil was composed of several miles of very thin insulated copper wire wound around, and well insulated from, the primary coil, making a very high resistance, sparks would fly across the coil ends and a current of over thirty thousand volts was produced. To-day we call this an oscillating current, and we find it high potential because of its enormous voltage, and high frequency because of its rapid motion — the oscillations moving at the rate of two hundred and thirty millions per second. This is the current which gives us wireless telegraphy and the X-rays. In the following chapters these five different currents will be separately treated, and we shall find how each is produced.

There is another way of producing a slight electric current, however, and that is, by extreme variations of temperature. This is called the thermo-electric current, but has never been put to practical use because it is too weak. Such a current may be produced by running copper and iron bars alternately through holes drilled in the sides of a box, and joining their ends so that they are connected in series, and then forcing an extreme cold blast of temperature against one side of the box and applying heat to the other ends. The current will be derived from the free end of the first wire or bar placed in the box and the last bar, and if an electric bell is connected with these two ends the current will be strong enough to ring it.

Chapter IV. The Alternating Current And The Pulsating Current

We have found how a coil of wire, when revolved

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between the north pole and the south pole of a horseshoe magnet, cuts the lines of force and creates an alternating current wave. A dynamo is built upon this n ffiliis

FIGURE V.

principle, and has been made a practical producer of electricity by Thomas Edison and by S. P. Thompson. In Thompson's own work : "The dynamo electric machine is a machine for converting energy in the form of mechanical power into energy in the form of electric currents, or vice versa, by the operation of setting conductors (usually in the form of coils of copper wire) to rotate in a magnetic field."

FIGURE VI.

In Fig. IV we have an imaginary view of an alternating current wave with a center line, marked off in degrees. And in Figure V we see the imaginary lines of force stretching between the north

FIGURE VII.

pole of a magnet and the south pole of another magnet. Figure VI. shows a coil of thin wire inserted between these two permanent magnets, exactly in line with these lines of force. When this coil of wire is moved thirty degrees of a revolution it has begun to cut these lines, and when it has moved ninety degrees it has cut the greatest number of lines of force within its field, and the coil of wire is perpendicular to these lines, as shown in Figure VII. Then as the coil is kept revolving it comes again in line with these lines as it reaches one hundred and eighty degrees, and when it has been revolved two hundred and seventy degrees our coil again cuts the greatest number of these invisible lines in the field, and finally comes back to its original position, after it has been revolved three hundred and sixty degrees of a circle. During each revolution, then, we see the induced voltage rises from zero to maximum, then decreases, then reverses, then rises to maximum in the opposite direction, and decreases to zero again. If we connect a telephone receiver between the two free ends of this coil of wire, as shown in the drawings, we can detect the current generated as we revolve the coil.

When we wind our coil on an iron core, through the center of which has been drilled a hole with a tightly fitted axle inserted therein, perpendicular to the length of the core, and upon this axle place a fiber insulating spool near one end, and over this spool fit a brass collar, we can make an armature by connecting one end of the coil to the brass collar and the other end to the iron core. Upon this principle is the so-called magneto made, which has one metal brush rubbing against the collar and another such brush rubbing against the axle of the core. When such a machine is made to run swiftly by power we can pick off these alternating current waves from the two brushes, and produce a voltage of electricity. A volt generated thus is equal to the armature coil cutting one hundred million lines of force per second. And the number of lines of force in the field of a horseshoe magnet varies in proportion to the strength of the magnet. So we see the stronger the field of a dynamo and the faster the armature is revolved within this field, the greater will be the voltage.