Electricity produces an infinity of changes in the natural world. It may
be artificially elicited or called forth by friction; or by contact of
certain substances and the action attendant on this contact. In the one
case it is termed ordinary, and in the other case voltaic or galvanic
electricity.
All substances are supposed to contain a certain portion of electricity,
and if by friction or other means any substance acquires more electrical
action than it would naturally possess, it is said to be positively
electrified; and if less, it is said to be negatively electrified.
Substances when positively electrified attract or draw toward them other
substances which are in a state of negative electricity, or even those
which are in a natural state, but will repel or force from them
substances which are positively electrified. The sudden contact of
bodies in an opposite state of electricity is attended with vivid light
called the “electric spark,” and accompanied by explosion and shock.