Radio Broadcast (May-Oct 1922)

152 RADIO BROADCAST any point in a second. It is represented by the letter "n." Suppose now that we wished to know how fast the waves are travehng. We could find this out in different ways. The easiest way to find it out is to figure it out as follows: Suppose each wave is lo feet long and there was one wave passing per second. The wave must be travelling lo feet per second, then, in order to get by. If two waves per second passed, then the waves must be travelling 2 x lo feet = 20 feet per second. If there were 12 waves per second (n = 12) and each wave was 10 feet long {'k = ID feet) then the waves must be travelling 12 X 10= 120 feet per second. But 12 x 10 is the same as n x X so that the rate of travel (velocity) of a wave is n x X. Velocity is always represented by the letter " v" so that v — n\. Now we have a very good idea of what water waves are. We can sum it up by saying that water waves are rfxurring displacements of water, traveling at a definite velocity and having definite amplitude, length, and frequency. These waves carry energy. This is true of water waves, and if we say "disturbance" instead of "displacement of water" it would be true of any kind of a wave. Waves are a recurring disturbance, traveling at a definite velocity and having definite amplitude, length, and frequency. Waves carry energy. Each different kind of wave has a definite velocity. All kinds of radio communication is carried on by waves, called radio waves. The velocity of a radio wave is so great that it would go around the earth seven times a second if it could keep on going. That is a great speed. It is 186,000 miles in a second. In radio we do not measure distances in miles — we use meters (a meter is a few inches longer than a yard). The velocity of radio waves is 300,000,000 meters per second. This velocity is constant, so that in measuring radio waves, if we can find either the frequency or the length, we know the other. This is true because v = nX and v is always equal to 300,000,000 meters per second. So if we know either n or X, the other one can always be obtained by dividing the known one into 300,000,000. Examples: (i) What is the frequency if X is 2,000? The frequency is 300,000,000 divided by 2,000=150,000 waves per second. (2) What is the wave length if the frequency is 50,000? X = 300,000,000-^ 50,000 = 6,000 meters. Sometimes one is stated and sometimes the other. Both are known when one is, as we have just shown. In order to have a wave it is evident that there must be some material to carry the wave. This thing in which the wave travels is called the medium. The medium that carries water waves is water. Sound is carried by waves in air. Air is the medium for sound waves. So for radio waves there is a medium which carries them. This medium is called the ether. Not much is known about the ether except that it will carry certain waves very rapidly. Besides carrying radio waves, it carries light waves and also heat waves. Another fact that is known about the ether is the fact that it is everywhere. It is between you and every other object. It is between the earth and the sun, the moon, and the sun, etc. It is in everything, as well as in the space outside. It is in the magazine you are reading — it is in your body. It is everywhere. There is no exception to that. You cannot think of a place where there is no ether — for there is no such place. Radio waves, then, are carried by this ether. In order to describe these radio waves it is necessary to recall and explain some simple facts that are familiar. In combing your hair, have you ever noticed that sometimes the hair will follow the comb as it passes back over the head, even though the hair and comb do not touch? This is explained by the fact that the comb has been electrified. The comb attracted the hair, causing it to move. How does one object move another when there is no apparent connection between them? The lack of connection in this case is only apparent and not real. There is a real connection between the comb and the hair which is not visible to the eye. A large number of invisible lines of force pass from the comb to the hair. These lines of force have a peculiarity in that they always try to become shorter. In trying to shorten they move the hair toward the comb. The complete name of these lines of force is electrostatic lines of force, the name coming from the fact that the lines have power and are caused by stationary (static) electricity (electro). Electrostatic lines of force are present in a radio wave. No doubt you have often pla>'ed with a magnet and noticed that the magnet will attract pieces of iron even though it does not touch them. Bring a magnet near a nail and suddenly the nail will jump to the magnet.