The ordinary garden variety of atom is made up of assorted particles of electricity.  In the center is a particle of positive electricity called the nucleus, and around this circulate one or more particles of negative electricity called electrons, in about the same manner as the planets in our solar system revolve about the sun.

The thing to keep in mind about these various particles is that there are strong forces of attraction and repulsion connected with them.  For example, a positive nucleus has more attraction for a negative electron  then a throbbing crooner has for bobby-soxers, but two negative electrons  or two positive nuclei simply can't stand the sight of each other any more than two women wearing identical dresses.

Ordinarily, the positive charge of the nucleus electron and the negative charge of an atom in exact balance, but sometimes an atom loses one of its electrons and so becomes slightly positive, in which case it is called a positive ion.  If,   on the other hand, it becomes slightly negative by picking up an extra electron, it is called a negative ion.  In either case, the atom is said to be ionized.

An atom that has lost one of its electrons and becomes positive has no morals at all, for it will steal any loose electron it can from a neighboring atom.  This state of affairs makes it possible for an electron with an itching foot to swing along from one atom to another; and when we have enough of these electrons all traveling in the same direction for an appreciable length of time, we have an electric current.

Some materials give up electrons easily and allow them to move about when attracted electrically.  Called good conductors, such materials include most metals.  On the other hand, there are substances which stubbornly hang on to their electrons and refuse to give up any appreciable of them, even under strong electrical pressure.  Materials of this kind, such as air, glass, and rubber, are called insulators.

The method by which electrons are persuaded to  move through a conductor is the application of an electromotive force (e.m.f.) across the ends of the conductor.  This electromotive force is produced in various ways, each of which produces a crowd of electrons at one end of a conductor and a scarcity of them at the other.  One of the most common is by the chemical action in a battery.  The chemical action is such that one terminal becomes positive and has a very strong attraction for negative electrons, and the other terminal becomes negative and is able to give up electrons very readily because it has a surplus of them.

When this battery is connected across a conductor, say a piece of wire, the electrons start slipping from the atoms near the positive terminal to that terminal.  These atoms, in turn, grab some electrons from their neighbors on the other side.  The neighbors do the same thing, and the process continues until the atoms at the negative end of the wire replenish their losses from the negative terminal of the battery.  This whole bucket-brigade movement of electrical charge takes place at terrific speed of nearly 300,000.000 meters per second.

Understand that a single electron does not zip from one end of the conductor to the other at this dizzy pace.  The movement is similar to that which takes place when the last one of a whole row of dominoes, standing on end right next to each other , is pushed over - the toppling movement flashes to the end of the row in a spilt second; yet each domino has moved but a short distance.

Each electron does drift slowly from one end of the conductor to the other, but its speed is much less and its path is much more erratic than that of the electrical charge itself.    If we could paint an individual electron a bright red and were able to follow its progress through the conductor, we would find it following as erratic a path as a pin-ball-machine marble and moving along at an average speed of about 1 foot in 11 seconds.  This is its linear speed through the conductor.  It whirls around the nucleus at 100 miles per second.

When the electrons move in a single direction through a conductor, we have direct current (d.c).  All batteries and some generators produce an e.m.f. resulting in d.c.  Other devices, especially certain kinds of generators, produce an e.m.f. that periodically reverses its direction;  the current that results from this type of voltage is called alternating current (a.c.)  Each terminal of such

  a generator keeps changing from positive to negative and back again, and the other terminal keeps changing its charge so as always to remain opposite to that of the first terminal.

The speed with which this voltage reverses may be from a few times a second to millions of times a second.  The portion of its action during which an a.c. voltage stars at zero, builds up to a peak in one direction, falls  to zero, builds up to peak in the opposite direction, and again falls to zero is called a cycle.  The number of cycles that occur in a second is the frequency  of the alternating current.  Most a.c. voltages furnished to residences are of the 60-cycle variety, and the diagram in Fig. 101 shows how a complete cycle takes place in 1/60 of a second.

To use electricity, we must be able to control it; and to secure control, we must have methods of measuring it.  The early physicists decided to establish a connection between the newly discovered electricity and the old established standards of weight; so they said that the amount of electricity required to deposit .001118 gram of silver from a standard solution of silver nitrate in water should be known as the coulomb.  If a coulomb of electricity - about 6.28 x 1018 (6,280,000,000,000,000,0000 electrons- flows past a given point in a second, a current of one ampere is said to be flowing.  A thousand of an ampere is termed a milliamperes.

The unit used to measure the resistance of a conductor to the flow of current is the ohm.  It was defined as the resistance offered to an unvarying electrical current by a column of mercury, 14.4521 grams in weight, at the temperature of melting ice, with a constant cross-sectional area, and 106.3 centimeters long.  The megohm, often used in radio work, is 1,000,000 ohms.

Once the ampere and the ohm have been determined, the volt, the unit of e.m.f. is easily defined.  It is simply the amount of e.m.f. that will cause a current of 1 ampere to flow through a resistance of 1 ohm.

And so we come to the end of the first chapter, and I still have not told you how to fix a radio; but do not be impatient.  If you have understood all the foregoing, you have established for yourself a solid foundation upon which a complete mastery of the theory and practice of radio can be built.