It will be well to keep clearly in mind that an electron is a real particle of negative electricity.
Electrons have been discovered only within recent years.
No matter from what substances we take them, they are always identical in every respect.
Some electrons are attached to the atoms of matter in such a way that they may be removed easily from one object to another.
When a surplus of these detachable electrons is crowded on to any object, we say that it is charged with negative electricity.
We speak of the other object, which has lost these same electrons, as being charged with positive electricity.
In this chapter the electron refers to the old-world experiment in which a piece of amber when rubbed attracts any light object to it.
For many ages man believed this to be a special property belonging to amber alone.
One of Queen Elizabeth's physicians discovered that this property was common to all substances.