Walter and the Wireless

by Sara Ware Bassett

"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."