factor soon assumes a religious
significance, and fire becomes sacred.

There are many conjectures respecting the discovery of fire. Probably
the two real sources are of lightning that struck forest trees and set
them on fire and the action of volcanoes in throwing out burning lava,
which ignited combustible material. Either one or the other, and
perhaps both, of these methods may have furnished man with fire.
Others have suggested that the rubbing together of dead limbs of trees
in the forests after they were moved by the winds, may have created
fire by friction. It is possible, also, that the sun's rays may have,
when concentrated on combustible {89} material, caused spontaneous
ignition. The idea has been advanced that some of the forest fires of
recent times have been ignited in this way. However, it is evident
that there are enough natural sources in the creation of fire to enable
tribes to use it for the purposes of artificial heat, cooking, and
later, in the age of metals, of smelting ores.

There has always been a mystery connected with the origin and use of
fire, which has led to many myths. Thus, the Greeks insisted that
Prometheus, in order to perform a great service to humanity, stole fire
from heaven and gave it to man. For this crime against the authority
of the gods, he was chained to a rock to suffer the torture of the
vulture who pecked at his vitals. Aeschylus has made the most of this
old legend in his great drama of _Prometheus Bound_. Nearly every
tribe or nation has some tradition regarding the origin of fire.
Because of its mystery and its economic value, it was early connected
with religion and made sacred in many instances. It was thus preserved
at the altar, never being allowed to become extinct without the fear of
dire calamity. Perhaps the economic and religious ideas combined,
because tribes in travelling from place to place exercised great care
to preserve it. The use of fire in worship became almost universal
among tribes and ancient nations. Thus the Hebrews and the Aryans,
including Greeks, Romans, and Persians, as well as the Chinese and
Japanese, used fire in worship. Among other tribes it was worshipped
as a symbol or even as a real deity. Even in the Christian religion,
the use of the burning incense may have some psychological connection
with the idea of purification through fire. Whether its mysterious
nature led to its connection with worship, and the superstitio