"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——"