“When we put an electron in an electric field,
we say it is "pulled." We then have two rules: (a) charges make a field, and
(b) charges in fields have forces on them and move. The reason for this will be-
come clear when we discuss the following phenomena: If we were to charge a body,
say a comb, electrically, and then place a charged piece of paper at a distance and
move the comb back and forth, the paper will respond by always pointing to the
comb. If we shake it faster, it will be discovered that the paper is a little behind,
there is a delay in the action. (At the first stage, when we move the comb rather
slowly, we find a complication which is magnetism. Magnetic influences have to
do with charges in relative motion, so magnetic forces and electric forces can really
be attributed to one field, as two different aspects of exactly the same thing. A
changing electric field cannot exist without magnetism.) If we move the charged
paper farther out, the delay is greater. Then an interesting thing is observed.
Although the forces between two charged objects should go inversely as the
square of the distance, it is found, when we shake a charge, that the influence
extends very much farther out than we would guess at first sight. That is, the effect
falls off more slowly than the inverse square.”