CHAPTER VI.
THE RADIO TELEPHONE.
Back and forth through s.p.a.ce they talked for quite a time. The boys were jubilant. The despair of many inventors, the wireless or radio telephone appeared to be an accomplished fact. But they didn"t dream how much yet remained to be done. At length Mr. Chadwick told them to "hang-up" and come back to the workshop.
The boys were glad to do this for they were extremely anxious to learn something of the forces controlling this aerial method of conversation. So far, they had not the least understanding, beyond a general idea, of how the thing was done. Of the details by which Mr. Chadwick had worked out this radical departure in telephony, they knew nothing.
"Well, what did you think of it, boys?" asked Mr. Chadwick when they returned to the workshop.
"Wonderful, beyond anything I could have imagined," declared Jack.
"How far will it work?" asked Tom.
"That"s just the point," said Mr. Chadwick. "That"s where I"m at sea. I need a metal of greater conductivity than any attainable to get real results. The carbon that I am using does not throw off enough radio activity to produce a sufficient number of electric impulses to the atmosphere."
Jack and Tom looked puzzled.
"You don"t understand me I see," said Mr. Chadwick.
"No, I must say I don"t," said Jack; "you see----"
"It"s pretty technical," broke in Tom.
"Well, then I"ll try to explain to you, in simple language, the general principles of radio telephony," said Mr. Chadwick. "In the first place you know, of course, from your wireless studies, that an electric wave sent into the air will travel till it strikes something, such as an aerial."
"To use the old ill.u.s.tration, an electric impulse sent into the air spreads out in all directions just like the ripples from a stone chucked into a mill-pond," said Jack.
"That"s it," said Mr. Chadwick. "Now then, as you also know the wire telephone works by a metal disc in the receiver, vibrating in exactly the same way as does the microphone in the transmitter. According to the vibrations of the voice of the person sending the spoken message, the electric current along the wire, acted upon by the microphone in the transmitter, increases or decreases. This increasing and decreasing current acts on a thin metal disc or diaphragm in the receiver which is held to the ear of the person listening to the message."
"That"s plain sailing so far," said Jack. "For instance, when you say "Hullo" over a phone, the microphone or transmitter gets busy and records it in electrical impulses and shoots it all along the wire where the receiver picks it up and wiggles the metal disc inside it to just the same tune."
"That"s it exactly," said Mr. Chadwick. "Now we are ready to go a step further. Now, as this metal disc is attracted or released by the current coming over the wire, it compresses or rarefies the air between it and the ear-drum of the person to whose oral cavity it is held. In this way the sensation of the same sound as was spoken at the transmitter end is reproduced at the receiver end. In other words, the transmitter jerks and jumps just as the needle of a phonograph does in traveling over a record, and transmits these jerks and jumps over the wire to the metal disc which by aerial pressure on the ear drums of the receiver of the message, causes the aural membrane to translate the words, or vibrations along the nerves, to the brain.
"Following up this line," said Mr. Chadwick, "we find that the problem in radio telephony is the same as that met with in ordinary wire telephony. That is to say, we are required to cause a distant metal disc to repeat every inflection of the transmitter. But in the case of radio telephony the result is to be obtained by Hertzian waves, instead of by a current pa.s.sing through an insulated wire."
"The same sort of waves that are employed in wireless telegraphy?" asked Tom.
"Just the same, only in radio telephony we are confronted by a problem not met with in wireless telegraphy. We have not only to transmit sound, such as isolated dots and dashes, but to send through the air every rise and fall and inflection of the human voice just as it is recorded in the minute lines of a phonographic record.
"Experiments have shown that articulation, that is, understand, a speech, depends upon overtones and upper harmonies of a frequency of 5,000 or 8,000 or more."
"What do you mean by frequency?" asked Tom.
"Speaking in reference to radio telephony it means the number of electrical vibrations per second required to produce a certain sound. In electric currents 100 per second is a low frequency current, 100,000 per second is spoken of as high frequency. In early experiments with radio telephony it was found that the chief difficulty lay in obtaining a current of sufficiently high frequency to transmit the human voice, the currents used in wireless telephony being much too weak for this purpose.
"I had, therefore, to invent my own alternator, which is attached to that gasoline motor. There is a similar one in the shed from which you just talked with me."
"But why does radio telephony require a stronger current than wireless telegraphy?" Tom wanted to know.
"Because, up to the present, no way has been found of utilizing in radio telephony the entire energy of the electric waves sent out," replied Professor Chadwick. "Only the variations in the waves can be detected, or transformed into sound at the receiving end of a radio telephone system. Therefore an immense amount of electrical energy has to be manufactured in order that the voice vibrations may register their variations as powerfully as possible."
"What percentage of the electrical energy manufactured by a high frequency alternator can be transformed into variations of sound?" asked Jack.
"Not more than five to eight per cent. of the total energy. So therefore the waste is enormous. In wireless telegraphy, on the other hand, the entire energy radiated from a sending station can be picked up to the limit of the receiver"s capacity to detect it."
"Isn"t there any way in which this difficulty could be overcome?" inquired Tom.
"Yes, there is," said Mr. Chadwick, after a moment"s thought, "and I believe that I am the only man in the world employed with radio telephonic problems who knows of it."
"Why can"t you use it, then?" asked Jack.
"Because there are almost insurmountable difficulties in the way. There is a substance chemically known Z. 2. X. which, if it could be applied to purposes of transmission and detection, has such immense powers of electrical absorption that messages could be sent almost any distance, and with far greater economy of power than at present."
"How far can you send them now?" asked Jack.
"About five miles. At least I think so. I"m not even sure of that," was Mr. Chadwick"s reply.
But Jack was impatient to get back to Z. 2. X.
"Why can"t you use this Z. 2. X.," he questioned, "if it would practically wipe out your troubles in sending and receiving?"
"Because there is even less of it in the world than there is of radium," was the startling reply. "At present Z. 2. X. costs far more than radium. It is the most intensely radio-active stuff in the world. It is capable of being wrought into metal if anybody had ever found enough of it, but except for a small deposit in South Africa, which has been devoted to experimental purposes, n.o.body has any.
"But enough of that now. That is only a dream. I am anxious, though, to test out my present apparatus thoroughly, and to do it I shall need the help of you boys."
"In what way?" asked Jack.
"In giving it a thorough trial to ascertain over how great a s.p.a.ce I can transmit wireless speech."
"Are you going to put up another station outside the grounds?" asked Tom.
"No; I don"t want to attract attention to my experiments. You boys have a wireless telegraph outfit on your Wondership?"
Jack nodded. He was curious, as was Tom, to know the Professor"s plan. They did not have long to wait.
"I wish you would get the machine ready to install a radio-telephone outfit in its place. In that way I can gauge the limits of my invention without attracting undue attention, as everybody in this vicinity has seen you in flight and would imagine that you were merely taking a trip through the air."
"But can you get out an apparatus light enough for us to take up?" asked Jack.
"I am working on that now," said Mr. Chadwick. "I"ll have it ready in a week."
"We"ll be ready for you," promised Jack.
CHAPTER VII.
THE GREAT TEST.
A week later to the day on a sunshiny, windless morning, the Wondership was run out of its shed, glistening with new paint and with every bit of bright work burnished till it shone and sparkled like newly-minted silver. Amidships on the craft, the general construction of which is familiar to readers of foregoing volumes of this series, was a square metal box with small wires leading to long copper wires stretched from end to end of the Wondership"s body.
These long copper wires were to form the aerials by which the messages from Mr. Chadwick"s workshop were to be caught. The smaller wires underneath were connected with the metal work of the engine. These wires formed a "ground" similar to the kind employed in aerial wireless telegraphy.
The details of the Wondership having been fully described in the Boy Inventors" Flying Ship, we shall not enter here into any but a brief and general description of the craft. The Wondership, then, was a combination of dirigible balloon, automobile and boat. Her motive power was furnished by engines driven by an explosive volatile gas which was also used when occasion arose to inflate the bag of the balloon feature of her design. The gas was generated in the lower part of the craft"s semi-cylindrical metal body.
On land two big aerial propellers, geared to the engine, drove the Wondership swiftly along on four solid-tired wheels. When it was desired to take to the air the balloon bag, which was neatly folded on a framework supported by upright stanchions above the body of the car, was inflated by turning on a valve connecting with the gas tanks in the base of the body.
When the Wondership was intended to navigate the water she was driven by the same aerial propellers that afforded her motive power on land or in the air. She then became what may be called a hydromobile. If it chanced to be rough weather, special hermetically sealed panels could be drawn together, completely enclosing the body and making the craft a water-tight "bottle." Ventilation was provided in such a case by a hollow telescopic tube which reached twenty-five feet into the air. It was divided in two. Fresh air was drawn by a fan down one section, while the stale air in the "cabin" was forced out by a similar device up the other part of the tube. Stability was afforded by hollow pontoons, which worked on toggle joints, and could be raised or lowered as desired.
With the aid of Jupe, the gas bag was inflated to a point where only a slight additional quant.i.ty of gas would cause the craft to shoot upward to the sky. When all was ready a test of the instruments was made and they were found to be working perfectly. The powerful alternator on the Wondership was, of course, worked by the same motor that drove the big propellers.
"Well, I guess there"s nothing to keep you back now," said Mr. Chadwick, who looked pale and ill after his long days and nights of work on his invention.
"No, we"re as ready as we ever will be," said Jack, making ready to climb into the machine above which the big yellow balloon bag was billowing and sending impatient quiverings through the Wondership.
"I want you to promise me one thing, dad," said Jack, when he had climbed into the driver"s seat, in front of Tom, whose duty it was to look after the engine.
"What is that, my boy?" asked the inventor.
"That after this test, whatever the result may be, you will take a long rest."
"Yes, I will, I must," agreed his father. "I"ve been working too hard, I guess, but in the excitement of perfecting the radio telephone I hardly noticed it. But recently I"ve had dizzy spells."
"Two weeks" rest will make you well," declared Jack, as he adjusted the controls.
"Good-by and good luck," said his father.
Both boys waved their hands.
"All ready, Tom?" hailed Jack.
The other boy nodded and then turned on a valve so that with a hissing sound additional gas rushed into the bag. Jack pulled a lever. The big motors roared and a queer, sickly smell of burned gas filled the air. The propellers began to revolve slowly and then increased their speed till they became a mere blur.
"Dere she go! Gollyumption, dere she go!" cried Jupe, capering about.
As the old black spoke, the Wondership shot up like a rocket, tilting her nose slightly into the air. But the next moment Jack had her on an even keel. In an incredibly short s.p.a.ce of time those watching below saw her only as a glinting, golden speck against the blue sky, circling like some strange bird far above their heads.
"Now for the tests," said Mr. Chadwick, as he hastened to his workshop.
He set the big alternator at work at top speed. It droned like a gaunt bee. The inventor"s face, worn by his anxious vigils at his experiments, was as keen as a hawk"s, while he adjusted the instruments and placed his long, lean fingers on the tuning device.
Far above the earth Jack and Tom could look down upon a patchwork of villages, farms, green pastures, yellow grain fields and stretches of woodland. They were too far up to distinguish figures, but they could see the white steam of rushing trains along the railroad tracks, and even catch the sound of the engines" whistles.
Beyond glinted the blue of the sea flecked with sails and with here and there a steamer"s smoke smudging the horizon. Both lads were in high spirits. It seemed good to be navigating the air again. Every now and then inquisitive, high-flying crows would swoop toward the machine and then dash off again with alarmed squawks.
Although they were making a high rate of speed, they hardly seemed to be moving as they soared in long circles. To get a sense of rapid motion, stationary objects must be in sight. In the lonely air it was hard to tell that they were moving at all except by looking down at the earth which, as they rose, appeared to be rushing from them, as if it were sinking through s.p.a.ce.
But novel as all these sensations would be to an aerial novice, they were an old story to the boys. Jack devoted his attention to testing a new steering appliance he had equipped the craft with, and Tom watched his engines with an eagle eye to detect a skip or a "knock."
"How high now?" asked the young engineer after an interval.
Jack glanced at the barograph on the dashboard in front of him.
"Three thousand feet," he said.
"Might as well connect the alternator?" said Tom interrogatively.
Jack nodded, and Tom threw a lever which brought the generator of high frequency currents in contact with the motor by means of a friction fly-wheel. The alternator began to buzz and spark, crackling viciously.
A sort of metal helmet with two receivers attached to it, one on each side, lay handy at Jack"s hand. In front of him was the transmitter joined to the metal box which contained the microphone, transformers and inductance tuning coil. Tuning in the aerial apparatus was effected by means of a small k.n.o.b projecting through a slit in the metal box enclosing the delicate instruments including the detector. By working this k.n.o.b the tuning block was moved up and down the coil till a proper "pitch" was obtained.
Jack experienced an odd thrill as he prepared to send the first spoken word ever exchanged between an airship in motion and a station on land. He and Tom had sent plenty of wireless messages while soaring through the ether, but somehow, the dot and dash system had not half the fascination and mystery of the possibility of exchanging coherent speech between land and air.
He placed his lips close to the receiver, and with his hand on the tuning k.n.o.b sent forth a loud, clear hail: "Hullo, High Towers!"
There was no answer for a few seconds while he patiently adjusted the tuning k.n.o.b. But then came a faint buzz like the humming of a drowsy bee. Suddenly, sharp and distinct, as if his father was at his elbow, came Mr. Chadwick"s voice in reply: "Hullo!"
"This is the Wondership. Three thousand feet in the air," cried Jack.
"Congratulations, my boy. It"s a success so far."
"What shall we do now?" asked Jack.
"I want you to fly in the direction of Rayburn, and try to keep in communication all the way."
"All right, dad," responded Jack, and altered the course of the Wondership.
Rayburn was a small village some twenty-five miles to the north of Nestorville. Jack kept the receivers on his ears as he flew along. From time to time he exchanged conversation with his father. So far everything appeared to be working as if there were no limit to the distance over which the voices from the air and land could converse.
But suddenly there came a startling interruption to the experiments.
Jack felt a sharp "Bang" at his ears as if a small cannon had been fired close at hand.