With advancing thought the ideas of polytheism later gave place to the
nobler conception of monotheism. But for a long time yet the same ideas
of the supernatural, as related to the natural, retained their place in
man's philosophy. Those phenomena which he thought he could understand
were looked upon as natural, while those which he could not understand
were looked upon as supernatural, and as produced by the direct personal
activity of some divine agency. As the centuries passed, and man's power
of observation became keener and his thinking more logical, many of the
hitherto mysterious phenomena became intelligible and subject to simple
explanations. As fast as this occurred these phenomena were
unconsciously taken from the realm of the supernatural and placed among
natural phenomena which could be explained by natural laws. Among the
first mysteries to be thus comprehended by natural law were those of
astronomy. The complicated and yet harmonious motions of the heavenly
bodies had hitherto been inexplicable. To explain them many a sublime
conception of almighty power had arisen, and the study of the heavenly
bodies ever gave rise to the highest thoughts of Deity. But Newton's law
of gravitation reduced the whole to the greatest simplicity. Through the
law and force of gravitation these mysteries were brought within the
grasp of human understanding. They ceased to be looked upon as
supernatural, and became natural phenomena as soon as the force of
gravitation was accepted as a part of nature.

In other branches of natural phenomena the same history followed. The
forces and laws of chemical affinity were formulated and studied, and
physical laws and forces were comprehended. As these natural forces were
grasped it became, little by little, evident that the various phenomena
of nature were simply the result of nature's forces acting in accordance
with nature's laws. Phenomena hitherto mysterious were one after another
brought within the realm of law, and as this occurred a smaller and