Letters of a Radio-Engineer to His Son by John Mills My Dear Son: You are interested in radio-telephony and want me to explain it to you. I'll do so in the shortest and easiest way which I can devise. The explanation will be the simplest which I can give and still make it possible for you to build and operate your own set and to understand the operation of the large commercial sets to which you will listen. I'll write you a series of letters which will contain only what is important in the radio of to-day and those ideas which seem necessary if you are to follow the rapid advances which radio is making. Some of the letters you will find to require a second reading and study. In the case of a few you might postpone a second reading until you have finished those which interest you most. I'll mark the letters to omit in this way. All the letters will be written just as I would talk to you, for I shall draw little sketches as I go along. One of them will tell you how to experiment for yourself. This will be the most interesting of all. You can find plenty of books to tell you how radio sets operate and what to do, but very few except some for advanced students tell you how to experiment for yourself. Not to waste time in your own experiments, however, you will need to be quite familiar with the ideas of the other letters. What is a radio set? Copper wires, tinfoil, glass plates, sheets of mica, metal, and wood. Where does it get its ability to work-that is, where does the "energy" come from which runs the set? From batteries or from dynamos. That much you know already, but what is the real reason that we can use copper wires, metal plates, audions, crystals, and batteries to send messages and to receive them? The reason is that all these things are made of little specks, too tiny ever to see, which we might call specks of electricity. There are only two kinds of specks and we had better give them their right names at once to save time. One kind of speck is called "electron" and the other kind "proton." How do they differ? They probably differ in size but we don't yet know so very much about their sizes. They differ in laziness a great deal. One is about 1845 times as lazy as the other. That is, it has eighteen hundred and forty-five times as much inertia as the other. It is harder to get it started but it is just as much harder to get it to stop after it is once started or to change its direction and go a different direction. The proton has the larger inertia. It is the electron which is the easier to start or stop. How else do they differ? They differ in their actions. Protons don't like to associate with other protons but take quite keenly to electrons. And electrons-they go with protons but they won't associate with each other. An electron always likes to be close to a proton. Two is company when one is an electron and the other a proton but three is a crowd always. It doesn't make any difference to a proton what electron it is keeping company with provided only it is an electron and not another proton.... We are delighted to publish this classic book as part of our extensive Classic Library collection. Many of the books in our collection have been out of print for decades, and therefore have not been accessible to the general public. The aim of our publishing program is to facilitate rapid access to this vast reservoir of literature, and our view is that this is a significant literary work, which deserves to be brought back into print after many decades. The contents of the vast majority of titles in the Classic Library have been scanned from the original works. To ensure a high quality product, each title has been meticulously hand curated by our staff. Our philosophy has been guided by a desire to provide the reader with a book that is as close as possible to ownership of the original work. We hope that you will enjoy this wonderful classic work, and that for you it becomes an enriching experience.