S OF A RADIO-ENGINEER TO HIS SON

LETTER 1

ELECTRICITY AND MATTER

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 dire