change is the eternal motion of the air.

Diogenes of Apollonia, in Crete, one of the disciples of Anaximenes,
born 500 B.C., also believed that air was the principle of the
universe, but he imputed to it an intellectual energy, yet without
recognizing any distinction between mind and matter. He made air and
the soul identical. "For," says he, "man and all other animals breathe
and live by means of the air, and therein consists their soul." And as
it is the primary being from which all is derived, it is necessarily an
eternal and imperishable body; but as _soul_ it is also endued with
consciousness. Diogenes thus refers the origin of the world to an
intelligent being,--to a soul which knows and vivifies. Anaximenes
regarded air as having life; Diogenes saw in it also intelligence. Thus
philosophy advanced step by step, though still groping in the dark; for
the origin of all things, according to Diogenes, must exist in
_intelligence_. According to Diogenes Laertius, he said: "It appears to
me that he who begins any treatise ought to lay down principles about
which there can be no dispute."

Heraclitus of Ephesus, classed by Ritter among the Ionian philosophers,
was born 503 B.C. Like others of his school, he sought a physical ground
for all phenomena. The elemental principle he regarded as _fire_, since
all things are convertible into it. In one of its modifications this
fire, or fluid, self-kindled, permeating everything as the soul or
principle of life, is endowed with intelligence and powers of ceaseless
activity. "If Anaximenes," says Maurice, not very clearly, "discovered
that he had within him a power and principle which ruled over all the
acts and functions of his bodily frame, Heraclitus found that there was
life within him which he could not call his own, and yet it was, in the
very highest sense, _himself_, so that without it he would have been a