They eyed it with intense curiosity, not unmixed with awe. They had already heard and read enough of the wireless telephone to realize that it was one of the greatest marvels of modern times. It seemed almost like something magical, something which, like the lamp of Aladdin, could summon genii who would be obedient to the call.

The rooms were comfortably filled when Dr. Dale, with a genial smile, rose and took up his stand near the table.

"Now, boys," he said, "I've asked you to come here to-night so that we can talk together and get a little better idea of some of the wonders of the world we are living in. One of those wonders and perhaps the most wonderful of all is the wireless telephone," and here he laid his hand on the box beside him. "Most of you have heard of it and want to learn more about it. I'm going to try to explain it to you just as simply as I possibly can. And I'm not going to do all the talking either, for I want you to feel free to ask any questions you like.

And before I do any talking worth mentioning, I'm going to give you a little idea of what the wireless telephone can do."

The boys watched him breathlessly as he handled two of the k.n.o.bs at the side of the box. A moment later they heard the clear, vibrant notes of a violin playing a beautiful selection from one of the operas. The music rose and swelled in wonderful sweetness until it filled the room, with the delicious melody and held all the hearers entranced under its spell. It was evident that only the hand of a master could draw such exquisite music from the instrument.

The doctor waited until the last notes had died away, and smiled with gratification as he saw the rapt look on the faces of his visitors.

"Sounds as if it were in the next room, doesn't it?" he asked.

"But that music came from Newark, New Jersey."

"Gee," whispered Jimmy to Bob, alongside whom he was sitting, "that's nearly a hundred miles from here."

"But there's no need of confining ourselves to any place as near as that," continued the doctor. "What do you say to listening in on Pittsburg? That's only a trifle of four hundred miles or so from here."

"He calls four hundred miles a trifle!" breathed Jimmy. "Pinch me, somebody. I must be dreaming."

Joe on his other side pinched him so sharply that Jimmy almost jumped from his chair.

"Lay off there," he murmured indignantly.

"S-sh," cautioned Bob, for by this time the doctor had made another adjustment.

Then into the room burst the stirring strains of the "Stars and Stripes Forever" played by a band that had a national reputation.

The rhythm and dash and fire of the performance were such that the boys had all they could do to keep their seats, and, as it was, their feet half unconsciously beat time to the music.

"Hit you hard, did it?" smiled Dr. Dale, who, to tell the truth, had been keeping time himself. "Well, I don't wonder. I'd hate to see the time when music like that wouldn't shake you up. But now we'll go a few hundred miles farther and see what Detroit has to give us."

Jimmy was past speech by this time and could only look at his comrades in helpless wonder. Then the tw.a.n.g of a banjo sounded through the rooms and to the thrumming of the strings came a voice in rich negro dialect

"It rained all night the day I left, The next day it was dry, The sun so hot I froze to death Susanna, don't you cry."

CHAPTER IV

MYSTERIOUS FORCES

The boys broke out in roars of laughter in which the doctor joined heartily.

"You see how it is," he said, as the song came to an end. "There's hardly anything you can think of that you can't hear over the wireless telephone. It takes you anywhere you want to go in a fraction of a second. In the last few minutes, we've covered quite a section of the United States, and with a still stronger instrument we could go right out to the Pacific coast and hear the barking of the sea lions at the Golden Gate."

"Wonder if we could hear the barking of the hot dogs at Coney Island,"

whispered the irrepressible Herb, who would have his joke.

Bob nudged him sharply and Herb subsided.

"And you can pick out any kind of entertainment you want," the doctor went on. "The great stations from which this music was sent out have programs which are published every day, together with the exact time that the selections will be given. At a given minute you can make your adjustment and listen to a violin solo, a band concert, a political speech, a sermon, or anything else that you want. If it doesn't please you, you can shut it off at once, which is much easier and pleasanter than getting up and going out from an audience.

"We'll have some more selections later on in the evening," he continued, "but now I want to explain to you how this thing is done.

I can't hope to do much more than touch the surface of the subject to-night, for I don't want to tire you out, and there'll be plenty of other nights and days when I hope you boys will call upon me for any information that you want and I can give.

"Of course the whole thing is based on electricity, the most wonderful thing that perhaps there is in the whole physical world. n.o.body knows what electricity is--Mr. Edison himself doesn't know. We only know that it is a wonderful fluid and that the ether is full of it. But though we don't know what it is, scientific men have learned how to develop and use its energy, and among other things they have harnessed it in the service of the wireless telephone.

"Take for instance a quiet lake. It may seem absolutely still, but if you throw a stone in it you start a number of ripples that keep spreading further and further out until they break on the sh.o.r.e. So if you hit a drum with a stick, sound waves are stirred up that keep spreading out very much like the ripples on the lake.

"Now electricity is something like that. It doesn't begin to act until you do something to it. The impulse to ripple is in the quiet lake all the time, but it doesn't ripple until you throw the stone in it. The sound quality is in the drum, but you don't hear it until you hit the drum with a stick. So you've got to put into the ether something that disturbs the electricity in it, something that stirs it up, and then this disturbance makes waves that travel on, just as the waves on the lake follow one another and just as the sound waves from the drum keep pushing each other along.

"A man named Hertz discovered a way of stirring up this energy, snapping it, you might say, as a man snaps a whip. It was found that these waves could be made long enough and strong enough to go all the way across the Atlantic Ocean, in fact to go around the world.

"Around the world!" murmured Jimmy, and again he was tempted to ask somebody to pinch him, but remembered his previous experience and stopped just in time.

"Now," continued the doctor, "you may ask what this has to do with the voice, for it is with the voice that one talks over the 'phone.

The whole principle of the wireless telephone is based on the fact that sound can be transformed into electricity and then can be transformed back into sound again. I know," he said, with a smile, "that that sounds very much like saying that you can make eggs into an omelet and then get the omelet back into separate eggs again"--here there was an audible snicker from the boys--"but that is very much like what is done by the wireless, although it doesn't exactly fit the case.

"Now see what a wonderful increase in power you get the moment the sound waves are changed into electric waves. Sound goes at the rate of one thousand and ninety feet a second. Electrical energy travels at the rate of one hundred and eighty-six thousand miles a second.

In other words it could go around the world more than seven times in a single second.

"When you speak into a telephone, unless you are greatly excited, you don't use more than a fiftieth part of the power of your voice.

But by the time that sound has been caught up and churned, as it were, into electrical energy it is more than a hundred thousand times as loud and strong.

"Suppose now, just as an ill.u.s.tration, that you were going to telephone to Europe. You'd pick up the 'phone and give your message.

That sound would go in the form of a tiny electrical impulse into one of the great sending stations on the Atlantic Coast, we'll say, and there it would be caught up by a powerful lot of electrical machines, amplifiers, alternators, and others, that would keep making it stronger and stronger until finally it was flung out into s.p.a.ce from the ends of the great wires or antennae. Out and out it would go until it struck a lot of wires on the other side of the ocean. Then it would go through another process that would gradually change the electrical impulse back into sound again, and the man at the other end of the telephone would hear your voice, just as one does now when you 'phone to any one in this town."

He paused for a moment, and there was a long drawn breath on the part of his auditors that testified to the rapt attention with which they had followed him into this fairyland of science.

"So much for the theory and principle of the wireless," resumed the doctor. "Of course I've only scratched the surface, and if I talked to you all night there'd be still lots left to say. But we only need to know a little about it to put it to practical use. And it is the practical use of the wireless telephone that I'm especially interested in for the sake of you boys. I'm satisfied that there's hardly anything that could give you more pleasure or more benefit than for each of you to have one of these contrivances in your own home. It's a wonderful educator, it helps to develop your interest in science, and what will perhaps appeal to you most of all, you can have more fun with it than anything else I know of."

Here Bob put in a question that was in the minds of many of the others.

"Does it cost very much, Doctor?" he asked.

"Not very much," the doctor replied. "Of course, some of the more powerful ones with vacuum tubes and other high cla.s.s improvements run into the hundreds of dollars. But some very good receiving sets--and that's all you could use at the start, for it takes considerable time and you have to get a license before you are permitted to transmit--cans be bought for from twenty-five to seventy-five dollars."

There was a little gasp at this, some of which was due to a feeling of disappointment. It seemed beyond the range of what they could save up from their pocket money, and while the parents of some of them were well to do, others came from simple and frugal homes where every dollar had to be carefully counted.

The doctor was quick to note the expression on many faces, and took pains at once to remove any feeling of discouragement.

"But don't let that bother you at all," he said, "for with a little thought and planning any one of you will be able to build a telephone receiving set for himself at hardly any cost at all. In fact, I'd much rather have you build one than buy one, for in that way you'll get an understanding of the whole thing that otherwise you might not get at all. You'd be surprised perhaps if I told you that this set here was built by me and I wouldn't exchange the experience I've had in putting it together for a good deal of money."

"But you knew how to do it," put in Joe, "while we don't know the first thing about it. We wouldn't know how to start, even, let alone finish one."

"I was coming to that," returned Dr. Dale, smiling. "As some of you know, I've fitted up a workshop in the barn behind this house where I do a good deal of tinkering in my spare hours. Now I'm going to ask you boys to come out there next Sat.u.r.day and see me build a wireless receiving set from A to Z. You'll be surprised to see how much can be done with a few things that cost very little money and with a lot of things that don't cost any money at all. How about it, boys?"