orn, marrow, blood, &c. This
doctrine implied that in compound things there was not a formation, but
an arrangement. It required, therefore, many elements instead of a
single one. Flesh is made of fleshy particles, bones of bony, gold of
golden, lead of leaden, wood of wooden, &c. These analogous constituents
are homoeomeriae. Of an infinite number of kinds, they composed the
infinite all, which is a mixture of them. From such conditions
Anaxagoras proves that all the parts of an animal body pre-exist in the
food, and are merely collected therefrom. As to the phenomena of life,
he explains it on his doctrine of dualism between mind and matter; he
teaches that sleep is produced by the reaction of the latter on the
former. Even plants he regards as only rooted animals, motionless, but
having sensations and desires; he imputes the superiority of man to the
mere fact of his having hands. He explains our mental perceptions upon
the hypothesis that we have naturally within us the contraries of all
the qualities of external things; and that, when we consider an object,
we become aware of the preponderance of those qualities in our mind
which are deficient in it. Hence all sensation is attended with pain.
His doctrine of the production of animals was founded on the action of
the sunlight on the miry earth. The earth he places in the centre of
the world, whither it was carried by a whirlwind, the pole being
originally in the zenith; but, when animals issued from the mud, its
position was changed by the Intellect, so that there might be suitable
climates. In some particulars his crude guesses present amusing
anticipations of subsequent discoveries. Thus he maintained that the
moon has mountains, and valleys like the earth; that there have been
grand epochs in the history of our globe, in which it has been
successively modified by fire and water; that the hills of Lampsacus
would one day be under the sea, if time did not too soon fail.

[Sidenote: Doubts whether we have any criterion of truth.]

As to the nature of human knowledge, Anaxagoras, asserted that by the
Intellect alone do we become acquainted with the truth, the senses being
altogether untrustworthy. He illustrated this by putting a drop of
coloured liquid into a quantity of clear water, the eye being unable to
recognize any change. Upon such principles also he asserted that snow is
not white, but black, since it is composed of water, of which the colour
is black; and