Chapter 14

BOB AS PEDAGOGUE

The wireless was now in commission and the next morning, after having waited until the hour designated for O'Connel's signal and received no message, Bob and his pupils assembled for their first lesson, not in a stuffy room but on the broad, well-shaded veranda of Surfside. A cool breeze rippled the water, stirring it into tiny waves and as Dick dropped into one of the big wicker chairs he fidgeted to be out in the freshly-painted knockabout that bobbed invitingly at the float.

His father intercepted his yearning glance and instantly interpreted it.

"Come, now!" said he half playfully. "Quit making sheep's eyes at that boat, son. An hour's wireless lesson isn't going to cut your morning very short or prevent you from having plenty of time to sail, swim, or motor. Whether it does or not you've got to endure it. Your summer holiday is long enough in all conscience. If I had until October with nothing more arduous to do than put up with an hour's instruction early each day I should think myself almighty lucky."

"I am lucky, Dad," conceded Dick quickly, "only----"

"Lucky! I should say you were! You don't know what work means. Well, it was you who wanted this radio outfit. You were all for it and----"

"I am for it still, Dad," interrupted Dick eagerly.

"Then go to it and master it," retorted his father. "If you do not relish the lessons swallow them down for the sake of the fun you are going to have later; for if you are intelligent enough to handle your wireless with some brain and understanding you are going to enjoy it a hundred per cent. more in the end."

"I know I shall," Dick agreed. "It is only that I am crazy to get at the thing itself."

The boy's father shook his head.

"You are like all your generation," said he severely. "Eager to leap the preliminaries and land at the top of the ladder with the first bound. It is an impatient age and the vice extends to the old as well as the young. Nobody wants to fit himself for anything nowadays. In my youth men expected to serve apprenticeships and did not hope to achieve a position until they had learned how to fill it. But now everybody leaps at the big job and the big salary that goes with it and blunders along, taking out his ignorance and lack of experience on the general public. As for you youngsters, you covet at fifteen everything that those who are fifty have. You want automobiles, boats, victrolas and radio telephones before you know how to run them, much less pay for them. Look at Bob, here. He is worth two of you for he can earn what he has. Often I tell myself I am a fool to indulge you and Nancy as I do. I ought by rights to make you do without what you want until you can foot the bill for it." Mr. Crowninshield took a few hasty paces across the piazza. "Still," added he, his voice softening, "I fancy that scheme would be a sight harder on me than on you, for I like nothing better than to get you what you want."

For a moment he paused, looking fondly at his son. Then as if afraid of himself he bristled and continued: "But to return to this wireless--remember that if you do not learn something about it and how to use it I shall take it away. I mean it, mind!"

"Yes, Dad," was the timid answer.

With this awful alternative looming like a specter in his path was it to be wondered at that Dick resolutely turned his gaze from the allurements of the harbor and settled himself in the big chair with all his attention focussed on Bob King's radio lesson. Moreover, human nature is selfish enough to like company in its misery and were not his mother, Nancy and Walter consigned to the same fate as himself?

Therefore the initial lesson began gayly.

At first Bob, seated in the chair of state facing his class, was shy and embarrassed; but soon he forgot himself in his subject and losing his hesitancy he spoke with the authority of one who has mastered his art.

"I am going to begin," said he, "just as they began with me at the radio station for I think if you get the principles of wireless at the outset you will find it much easier to understand it. And to do this we shall not start with wires, generators, detectors, or anything of that sort; instead we must go back of them all to the earth and the air, and learn how it is possible for sound to travel without the aid of human devices. For in reality there is something that takes the place of man-made wires. This is the ether. Surrounding the earth moves the air we breathe; and as we go higher this air becomes thinner and thinner until, by and by, a height is reached where the air gives place to ether, a sort of radiant energy that bridges the zone between the air space that encircles the earth and the sun, and brings to us its heat. This great sea of ether is made up of particles that are never still and which are so small that they get between every substance they encounter, thereby becoming a universal medium for transmitting light, heat, color and many other things to our earth. Without this body of ether, there would be no agency to pass on to us (as well as to the many other planets of our solar system and those outside it) the energy the sun generates, which is the thing that keeps us alive."

Bob waited a moment to make sure that his point was clear and then proceeded:

"Now this energy as it moves through the ether takes the form of waves; and these waves go out not in a single train but since the ether is continually disturbed by the sun, in series of wave trains that vary in frequency. Such waves are electromagnetic in character, and light, heat, sound, and the waves carrying wireless messages are all of a similar type, differing only in their relative rates of vibration. If unobstructed, and moving through free ether, all of them travel at practically the same velocity, that is about one hundred eighty-six thousand miles a second. When, however, they encounter other substances, as they are continually bound to do, this rate of velocity changes. The waves of sound, for example, sent out by the wireless telephone are very slow compared with the high-rate vibrations that produce waves resulting in light."

Again the youthful teacher paused.

"Now this constant turmoil in the ether which creates the magnetic area explains why the magnetized needle of a compass unfailingly points north and south. This one simple fact is a certain proof of its existence. And once granting a magnetic field to be there it is less difficult to understand how wireless waves are produced in this congenial medium and find their way through it, following in their journey the curve of the earth's surface."

Bob smiled at his audience encouragingly.

"If you can once get this wave law through your heads the rest is not hard," asserted he, "for the whole wireless system is based on wave motion."

"With an ocean spread out before us we ought to be able to understand waves," interpolated Nancy.

"We ought," nodded Bob. "And yet better than using the ocean as an illustration imagine a small pond. Think, instead, of a nice quiet little round pond if you can. Now when you chuck a stick or a pebble into that still water you know how the ripples will at once go out. There will be rings of them, and the bigger they get the fainter they will be. In other words, as the area widens the strength of the waves decreases; and as this same principle applies to radio you can see that it takes a lot of energy from a wireless station to reach a receiver a great distance away."

"I've got that!" cried Dick with such spontaneity that every one laughed.

"Wave lengths, however, have nothing to do with actual distance," went on Bob quickly. "Of course we think of the wave length as the distance between one ridge of water and another. There is, though, no law that would make it possible to translate these spaces into our scale of miles, for sometimes they are near together, sometimes far apart. Distance, therefore, depends on the speed with which the wave travels and the frequency with which the water is disturbed. If you keep tossing things in quick succession into the water you will get a correspondingly quick succession of waves. The law governing wireless waves is exactly the same. Their length depends on the velocity of the wave and the frequency of the oscillations that cause it. Or to put it another way, in order to reckon a wave length you must determine its velocity (which is not impossible when you remember that sound travels about one thousand one hundred and twenty feet every second) and the number of vibrations the particular note causing the wave is making per second. Now science has been able to compute just how many complete vibrations a certain note, key, or pitch as you may please to call it, makes each second, or how many times the particles of air vibrate back and forth when that especial note is sent out.

"Suppose, for example, a note makes 240 complete vibrations a second while traveling 1,120 feet; if we divide 1,120 by 240 we shall get 4.66 as the wave length of this note. So it is the pitch to which a note is keyed that helps determine its distance; and the force employed to start the note sent out through the magnetic field. That is why a message projected into the ether from a high-power station carries a greater distance than one sent from a station where the power is weaker. It is by power and pitch, then, not by length that we gauge wireless waves. Do you see that?"

A chorus of assent greeted the question.

"That's bully!" Bob announced boyishly; then blushed at the undignified ejaculation.

"Don't you be fussed, young man," smiled Mr. Crowninshield. "We're all of an age here."

"I quite forgot," apologized the tutor.

"That is exactly what I want you to do," returned the master of Surfside. "Ignore us old people. We are only listening in, anyway, and have no earthly right to be here."

"Still, I wish to treat you with----"

"It's all right, Bob. We understand," put in Mrs. Crowninshield reassuringly.

"Well, then, if you will excuse me I'm off again," replied the boy. "And now that we've got wave lengths settled to our satisfaction we must remember some other things. One is that sound travels not only through the air but through the water. In fact, sounds are louder under water than they are above it. Water is not only a better medium for carrying sound but also, since it contains fewer obstructions, sound waves travel farther through it. Another thing which we must not forget is that our ears do not hear all the sounds that go on about us. The merciful Lord has arranged that when there are less than twenty-four vibrations a second, or more than forty thousand they escape us. But a wireless instrument, on the contrary is spared nothing, having attached to it a detector that catches every sound and an amplifier that magnifies it and makes it discernible to our ears. When you listen in on a wireless telephone you will be uncontestably conscious of this. Also you must take into consideration that the waves sent out by a radio transmitter are not choppy, irregular ones such as you get when a stone is tossed into the water; wireless waves go out in regular, well-formed relays that neither overlap nor obscure one another. Were this not so the signals made would be jumbled together and utterly unintelligible."

"Sure they would!" Bob's young brother nodded.

"Now to insure these several results we are compelled to resort to the help of scientific apparatus. Therefore at every receiving station we have devices that will intercept the waves as they come in; retransform them into electrical oscillations; and catching the weak oscillations make them strong enough to be read. Hence we use some type of induction coil by means of which a battery current of such low pressure and diffused flow as scarcely to be felt will be transformed or concentrated into a pressure that is very powerful. In order to form wireless waves we must have a frequency of at least one hundred thousand vibrations a second; and as it is out of the question to produce these by mechanical means we employ a group of Leyden jars. Such jars you have of course seen. They have in them two pieces of tinfoil separated by glass, which is a nonconductor of electric currents, and various other acids and minerals. When you connect a number of these small jars together you have a battery as powerful as that of a large single jar."

"I never saw jars like those," objected Dick.

Bob beamed at the intelligence of the demurrer.

"When I say jar," explained he, "it does not necessarily mean that these jars are of the round, cylindrical shape that comes to mind when you mention the word; on the contrary Leyden jars are often flat because such a form makes them more compact. That is also why we use several little ones instead of one big one. But whatever their shape the principle involved is always the same. When the terminals are connected with a current the jar will not only receive but will retain a charge equal in pressure to that of the device sending the current. And when you go even farther and bring the terminals near together, the quick discharge that takes place creates an electric spark which is in reality a series of alternating flashes that come so fast as to be blurred into what appears to be one. Could we separate these flashes we should find that each of them lasts less than a thousandth part of a second. The frequency of such oscillations is regulated by what is technically termed capacity, that is the size of the Leyden jar. The smaller the capacity the greater the frequency of the flashes.

"Now this spark, or oscillatory discharge emitted from the Leyden jar, does not result from a single traveling of the current all in one direction; instead the electricity moves back and forth, or alternates, and the space where the discharge takes place (and which, by the way, can be lengthened or decreased as pleases the operator) is known as the spark gap."

"But I should think this explosion of the spark would make a noise," commented Walter.

"Bully for you, little brother!" returned Bob, smiling at His Highness. "You are quite an electrician. If the current is strong, or, in other words, if the discharge is a high frequency one, it does. Hence something has to be used to deaden the sound just as a muffler is used on a motor boat. It is important, however, that this muffler should not prevent the operator from watching the condition of his spark for otherwise he could not keep track of his battery or know whether it was on the job or not. So you will find little peepholes of mica or glass in the sides of the muffler."

"Windows," murmured Nancy grasping the idea and translating it into the vernacular.

"Exactly," Bob agreed. Evidently his audience were understanding what he was trying to make clear to them.

"Now we have our high frequency oscillations occurring in the spark discharged from the Leyden jar and jumping the spark gap; nevertheless they would not do us any good were there not some way to use and regulate them. This brings us to the induction coil of which I spoke a second ago."

"It sounds very terrible," smiled Mrs. Crowninshield.

"It isn't, though," answered Bob, returning the smile. "In fact it is a very simple device--nothing more than a dozen or so twists of copper wire reeled about a wooden frame exactly as strands of thread might be wound round a spool. One end of the inductance is connected permanently with the ground and from the other end two movable wires go out, one of which can be connected with the spark gap and the other with the antenna that goes into the air and catches the sound waves. There isn't anything very terrible about that, you see."

"Antenna is what butterflies have," suggested Nancy vaguely.

"Quite right!" assented the wireless man. "Only radio antennæ are not to feel with--at least not in the same way. Nevertheless they do reach out and capture the sound. On all wireless stations you will notice the masts that support them. Sometimes there is one wire, sometimes a group. It is the wires themselves, remember, not the masts, which are the antennæ. Nowadays, however, you will occasionally see an indoor aerial used in connection with small, low-power outfits. It does away with the masts and outside equipment and frequently serves the same purpose quite satisfactorily. But most persons prefer the older method and for long-distance work it has, up to date proved to be indispensable. Now the antenna has both electrical capacity and inductance, and when connected up with the apparatus a wireless operator can at will cause it to disturb the magnetic fields surrounding the earth."

"You didn't say how high these masts had to be, Bob," put in Mr. Crowninshield. "Are they always the same length?"

"Oh, no, indeed, sir," was the prompt response. "Their length varies according to the type of service required of them. I'm glad you asked the question. Sometimes the masts are about two hundred feet high; again they may approximate four hundred and eighteen feet. And sometimes in emergencies you will discover no masts at all, the wires being fastened instead to captive balloons or kites which hold them in place long enough to send or receive hasty messages. This latter method is usually resorted to in wartime or during army or navy maneuvers. There are also compact radio sets to be had that can be carried on mule-back and set up and taken down on a hurried army march. On shipboard the ordinary masts of the vessel serve, of course, to support the antenna."

"Thank you, Bob. That is exactly what I wanted to know," said Mr. Crowninshield.

"I'm glad, sir. Now you'd think by this time we had everything necessary to produce our wireless waves and yet we haven't. There is still one thing almost more important than all the rest that we have not yet spoken of."

"What's that, Bob?" piped Walter.

"The tuner. You recall that at the beginning I mentioned the pitch, note, or key of the sound produced or received?"

"Yes," returned the class in chorus.

"Well, it is in that tune or pitch, or whatever you prefer to call it, that a large measure of the secret of wireless lies. To be successful in getting and sending messages we must tune the oscillations, or key the signals caused by the discharge of the battery in our Leyden jar, so that they will be in harmony (or at precisely the same pitch) with the antenna circuit. That is, the parts of the instrument must synchronize, just as two persons who would talk together must speak in the same language. This adjustment is made in the inductance coil because although both the Leyden jar where the spark is generated that causes the oscillations and the antenna can be regulated independently of each other a few turns of the inductance coil affects each circuit. After the two circuits have been adjusted to the same frequency they are said to synchronize. Often to reach this result a device is used that states precisely the wave length, and after the frequency of one circuit has been ascertained the other can easily be adjusted to correspond with it. The length of the wave is, you see, dependent on the largeness of the antenna and the capacity, or strength of current, of the Leyden jar. Just as a child uses a big stone to produce the largest splash and greatest waves so we must have a powerful force behind our wave lengths to make them carry most successfully. In accordance with this law, generally speaking, we find short wave lengths used for low power, short-distance outfits; and long wave lengths for high-power circuits whose aim is to traverse continents and oceans."

Bob pushed back his chair.

"I think," said he, "we have now come to a good stopping place and we will call the lesson off for to-day. If you digest all I have told you, you will have had an ample radio starter."

"You haven't said much about sending messages," complained Dick.

"That is quite another story," smiled the boy's tutor, "and such a long one that were I to tell it to you now it would mean you would get no sailing or swimming to-day."

Instantly Dick was on his feet, Leyden jars and inductance coils forgotten.

"We'll cut it out then," he laughed. "Who is for a swim? I'll race any man to the bath-house!" And off he went at top speed.