John Mills

“ The radio-telephone does not transmit the human voice. It reproduces near the ears of the listener similar motions of the air molecules and hence causes in the ears of the listener the same sensations of sound as if he were listening directly to the speaker. This reproduction takes place almost instantaneously so great is the speed with which the electrical effects travel outward from the sending antenna. If you wish to understand radio-telephony you must know something of the mechanism by which the voice is produced and something of the peculiar or characteristic properties of voice sounds. ”

“ That hydrogen atom is responsible for lots of interesting things for it is a great one to join with other atoms. We don’t often find it by itself although we can make it change its partners and go from one molecule to another very easily. That is what happens every time you stain anything with acid. A hydrogen atom leaves a molecule of the acid and then it isn’t acid any more. What remains isn’t a happy group either for it has lost some of its playfellows. The hydrogen goes and joins with the stuff which gets stained. ”

“ What gets away isn’t a sodium atom for it has one too few electrons; and what remains behind isn’t a chlorine atom for it has one too many electrons. We call these new groups “ions” from a Greek word which means “to go” for they do go, wandering off into the spaces between the water 20molecules. Fig. 3 gives you an idea of what happens.
You remember that in an atom there are always just as many protons as electrons. In this sodium ion which is formed when the nucleus of the sodium atom breaks away but leaves behind one planetary electron, there is then one more proton than there are electrons. ”

“ By proper number of electrons I mean proper for the number of protons which it has. If an ion has more electrons than protons it is negative; if the inequality is the other way around it is positive. An atom or molecule has neither more nor less protons than electrons. ”

“ You can see that there is always a little favoritism on the part of the grid-condenser detector. It doesn’t exactly reproduce the variations in intensity of the radio signal which were made at the sending station. It distorts a little. As amateurs we usually forgive it that distortion because it is so efficient. It makes so large a change in the current through the telephone when it receives a signal that we can use it to receive much weaker signals, that is, signals from smaller or more distant sending stations, than we can receive with the arrangement described in Letter 14. ”

“ If we should gradually increase the frequency of the alternating current you would find that about sixty or perhaps a hundred cycles a second would give you the impression of a musical note. As the frequency is made still larger you have merely the impression of a higher-pitched note until we get up into the thousands of cycles a second. ”

“ So the zinc atoms leave their places to join with the sulphate ions. But wait a minute! The sulphate ions have two extra electrons which they kept from the hydrogen atoms. They don’t need the two lonely electrons which each zinc atom could bring and so the zinc atom leaves behind it these unnecessary electrons.
Every time a zinc atom leaves the plate it fails to take all its electrons with it. What leaves the zinc plate, therefore, to go into solution is really not a zinc atom but is a zinc ion; that is, it is the nucleus of a zinc atom and all except two of the planetary electrons. ”

“ A short straight wire has a very small inductance, indeed. The longer the wire the larger will be the inductance but unless the length is hundreds of feet there isn’t much inductance anyway. A coiled wire is very different.
A coil of wire will have more inductance the more turns there are to it. That isn’t the whole story but it’s enough for the moment. Let’s see why. The reason why a stream of electrons has an opposing conscience when they are started off in a coil of wire is because each electron affects every other electron which can move in a parallel path. ”

“ Because the plunger in an alternating-current ammeter is soft iron its loops line up with those of the coil no matter which way the electron stream happens to be going in the coil. The atomic magnets in the iron turn around each time the current reverses and they are always, therefore, lined up so that the plunger is attracted. If the plunger has much inertia or if the oscillations of the current are reasonably frequent the plunger will not move back and forth with each reversal of the current but will take an average position. ”

“ If a telephone-receiver diaphragm can be made to vibrate in accordance with the variations in signal intensity then the air adjacent to that diaphragm will be set into vibration and these vibrations will be just like those which the human voice set up in the air molecules near the mouth of the speaker. All the different systems of receiving radio-telephone signals are merely different methods of getting a current which will affect the telephone receiver in conformity with the variations in signal strength. ”

“ It’s these wandering electrons which are affected when a battery is connected to a copper wire. Every single electron which is away from its home group, and wandering around, is sent scampering along toward the end of the wire which is connected to the positive plate or terminal of the battery and away from the negative plate. That’s what the battery does to them for being away from home; it drives them along the wire. ”

“ It means that two volts in the grid circuit have the same effect on the plate current as ten volts in the plate circuit. If we apply a volt to the grid circuit we get five times as large an effect in the plate circuit as we would if the volt were applied there. We get a greater effect, the effect of more volts, by applying our voltage to the grid. We say that the tube acts as an “amplifier of voltage” because we can get a larger effect than the number of volts which we apply would ordinarily entitle us to. ”

“ What sort of a molecule is formed will depend upon how many and what kinds of atoms group together to play the larger game. Whenever there is a big game it doesn’t mean that the little atomic groups which enter into it are all changed around. They keep together like a troop of boy scouts in a grand picnic in which lots of troops are present. At any rate they keep together enough so that we 7can still call them a group, that is an atom, even though they do adapt their game somewhat so as to fit in with other groups–that is with other atoms. ”

“ What I have just told you about electrons getting away from a heated wire is very much like what happens when a liquid is heated. The molecules of the liquid get away from the surface. If we cover a dish of liquid which is being heated the liquid molecules can’t get far away and very soon the space between the surface of the liquid and the cover gets saturated with them. ”

“ With 29 electrons it’s no wonder if sometimes one goes wandering off and finally gets into the game about some other nucleus. Of course, an electron from some other atom may come wandering along and take the place just left vacant, so that nucleus is satisfied.
We don’t know all we might about how the electrons wander around from atom to atom inside a copper wire but we do know that there are always a lot of them moving about in the spaces between 15the atoms. Some of them are going one way and some another. ”

“ Each gas is a different kind of atom. There is just a slight trace of hydrogen and a very small amount of helium and of some other gases which I won’t bother you with learning. Most of the air, however, is nitrogen, about 78 percent in fact and almost all the rest is oxygen. About 20.8 percent is oxygen so that all the gases other than these two make up only about 1.2 percent of the atmosphere in which we live. ”

“ Wherever you put up your receiving station you get more or less of this energy. Of course, energy is being sent out only while the key is depressed and the oscillator going. This energy travels just as fast as light, that is at the enormous speed of 186,000 miles a second. If you use meters instead of miles the speed is 300,000,000 meters a second.
Now, how far will the energy which is sent out from the antenna travel during the time it takes for one oscillation of the current in the antenna? Suppose the current is oscillating one million times a second. ”

“ If we are to talk about the audion and how its grid controls the current in the plate circuit we must know something of how to measure currents. An electric current is a stream of electrons. We measure it by finding the rate at which electrons are traveling along through the circuit. ”

“ The molecules of sulphuric acid dissociate in solution just as do those of copper sulphate. When sulphuric acid molecules split, the sulphate part goes away with two electrons which don’t belong to it and each of the hydrogen atoms goes away by itself but without its electron. We call each a “hydrogen ion” but you can see that each is a single proton.
In the two solutions are pieces of zinc and copper. Zinc is like all the rest of the metals in one way. Atoms of metals always have lonely electrons for which there doesn’t seem to be room in the game which is going on around their nuclei. ”

“ To get the most out of an audion see that the telephone, or whatever circuit or piece of apparatus is connected to the output terminals, shall have a resistance of RP ohms. When the resistance of the circuit, which an audion is supplying with current, is the same as the internal resistance of the output side of the tube, then the audion gives its greatest output. ”

“ You can see that as we make the grid more and more positive, that is, make it call louder and louder, a condition will be reached where it won’t do it any good to call any louder, for it will already be getting all the electrons away from the filament just as fast as they are emitted. Making the grid more positive after that will not increase the plate current any. That’s why the characteristic flattens off as you see at high values of grid voltage. ”

“ Sea water is mostly oxygen and hydrogen, about 85.8 percent of oxygen and 10.7 percent of hydrogen. That is what you would expect for water is made up of molecules which in turn are formed by two atoms of hydrogen and one atom of oxygen. The oxygen atom is about sixteen times as heavy as the hydrogen atom. However, for every oxygen atom there are two hydrogen atoms so that for every pound of hydrogen in water there are about eight pounds of oxygen. That is why there is about eight times as high a percentage of oxygen in sea water as there is of hydrogen. ”

“ The ends of this filament extend out through the glass so that we may connect a battery to them and pass a current of electricity through the wire. If we do so the wire gets hot.
What do we mean when we say “the wire gets hot?” We mean that it feels hot. It heats the glass bulb and we can feel it. But what do we mean in words of electrons and atoms? To answer this we must start back a little way.
In every bit of matter in our world the atoms and molecules are in very rapid motion. In gases they can move anywhere; and do. That’s why odors travel so fast. ”

“ There is still a great deal to be learned about how electrons act inside different kinds of atoms. We do know, however, that the atoms of iron act just as if they were tiny loops with electron streams. ”

“ I’ll tell you about wave lengths later. First let’s see how to control the frequency of an audion oscillator like that of Fig. 38.
It takes time to get a full-sized stream going through a coil because of the inductance of the coil. That you have learned. And also it takes time for such a current to stop completely. Therefore, if we make the inductance of the coil small, keeping the condenser the same, we shall make the time required for the current to start and stop smaller. That will mean a higher frequency for there will be more oscillations each second. ”

“ An efficient multi-stage amplifier for radio-frequencies is difficult to build because of what we call “capacity effects.”
Consider for example the portion of circuit shown in Fig. 127. The wires a and b act like small plates of condensers. What we really have, is a lot of 243 tiny condensers which I have shown in the figure by the light dotted-lines. If the wires are transmitting high-frequency currents these condensers offer tiny waiting-rooms where the electrons can run in and out without having to go on to the grid of the next tube. ”

“ Down in the bottom of the jar the hydrogen ions find more sulphate ions to play with, but that leaves the copper ions which used to play with these sulphate ions without any playmates. So the copper ions go still further down and join with the copper atoms of the copper plate. They haven’t much right to do so, for you remember that they haven’t their proper number of electrons. Each copper ion lacks two electrons of being a copper atom. Nevertheless they join the copper plate. The result is a plate of copper which has too few electrons. ”

“ Suppose the incoming signal has a frequency of 100,000 cycles a second but that the detector tube is oscillating in its own circuit at the rate of 99,000 cycles per second, then the listener will hear a note of 1000 cycles per second. One thousand times each second the two e. m. f.’s will be exactly in phase and one thousand times each second they will be exactly opposite in phase. The voltage applied to the grid will be a maximum one thousand times a second and alternately a minimum. ”

“ In my gravity battery the sulphate ions used to coax the zinc ions away into the solution. In the storage battery on the other hand the sulphate ions can get to most of the lead atoms because the lead is so spongy. When they do, they form lead sulphate right where the lead atoms are. They don’t really need whole lead atoms, because they have two more electrons than they deserve, so there are two extra electrons for every molecule of lead sulphate which is formed. ”

“ If you put a piece of it inside a coil which is carrying a steady current it becomes a magnet but about as soon as you interrupt the current the atomic loops of the iron stop pulling together. Almost immediately they turn into all sorts of positions and form little self-satisfied groups which don’t take any interest in the outside world. ”

“ A small copper wire will have in it billions of copper atoms, each with its planetary electrons playing their invisible game about their own nucleus. There is quite a little distance in any atom between the nucleus and any of the electrons for which it is responsible. There is usually a greater distance still between one atomic group and any other.
On the whole the electrons hold pretty close to their own circles about their own nuclei. There is always some tendency to run away and play in some other group. ”