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spool, a 25 [[cents]] crystal detector, and a pair of headphones, and I think my first set will consist of just that. I never shall get over the awe I always feel when I really stop to think about radio. It seems so marvelous to think that at this very moment electro-magnetic waves originating in, say Louisville, are pulsing through the space occupied by this room, and if I had the right instruments to detect and amplify them, I could hear your voice, providing you were broadcasting. Isn't it a marvelous thing? And all the more marvelous, when you think that the air is not only full of Louisville vibrations, but also the impulses emanating from a score or so other stations, all surging and pulsing together in a grand mixup; but we can pick out any one of them we want to, and hear only that one, merely by making our instruments more sensitive to that particular wave than to the others, I can't get away from the wonder of it.

[[underline]] To Mother, October 12, 1924: [[/underline]] Here is the explanation of my relay. You know that when [[underline]] too much [[/underline]] electric current flows through a motor or an incandescent lamp say, the thing will burn up -- the wires will melt. Therefore, they have to use some sort of a device for stopping the flow of current when it reaches a certain maximum value beyond which the lamp, say, would burn out. We will say we have an electric motor in a circuit and the circuit goes through the coil on the back of the panel. Well, as the motor is in the same circuit as the coil, the same amount of current flows through the coil as flows through the motor. When this amount of current reaches a certain value (the maximum safe current for the motor), the support (see drawing) becomes sufficiently magnetized (due to the current going through the coil) to pull over the arm D, which opens up the contact at K. When the contact at K opens, the "control circuit" is opened, that is, no more current flows in the control circuit and an automatic switch is opened in the main motor circuit, thus cutting off all current from the motor. The automatic switch I mentioned is called a "contactor," and I shall go on the assembly of those shortly. Of course, all that I described, happens almost instantaneously. Could you understand my explanation at all? It was a pretty poor one.

[[underline]] Note: [[/underline]] The photograph referred to above is on the next page.

[[underline]] To Mother, October 15, 1924: [[/underline]] You certainly must have a scientific mind to have thought out the operation of that relay all by yourself. Hereafter, I shan't hesitate to explain any piece of apparatus to you. All the relays operate on that same principle so I wont explain any more of them. ...... I am now reading Emerson's Essays -- what do you think of that? ...... George Zamzow just rigged up a little crystal set using the bed springs for an aerial, and got WGY so loud it nearly wrecked the earphones. ...... I finished assembling the "dollar an hour" job this afternoon -- 200 plungers for some relays -- but it wasn't