remains unharmed." As examples of essential properties, Lucretius
mentions "the weight of a stone, the heat of fire, the fluidity of
water." Such things as liberty, war, slavery, riches, poverty, and the
like, were accounted accidents. Time also was said to be an accident:
it "exists not by itself; but simply from the things which happen, the
sense apprehends what has been done in time past, as well as what is
present, and what is to follow after."

As our story proceeds, we shall see that the chemists of the middle
ages, the alchemists, founded their theory of material changes on the
difference between a supposed essential substratum of things, and
their qualities which could be taken off, they said, and put on, as
clothes are removed and replaced.

How different from the clear, harmonious, orderly, Greek scheme, is
any picture we can form, from such quotations as I have given from
their writings, of the alchemists' conception of the world. The Greeks
likened their imaginings of nature to the natural facts they observed;
the alchemists created an imaginary world after their own likeness.

While Christianity was superseding the old religions, and the
theological system of the Christian Church was replacing the
cosmogonies of the heathen, the contrast between the power of evil and
the power of good was more fully realised than in the days of the
Greeks; a sharper division was drawn between this world and another
world, and that other world was divided into two irreconcilable and
absolutely opposite parts. Man came to be regarded as the centre of a
tremendous and never-ceasing battle, urged between the powers of good
and the powers of evil. The sights and sounds of nature were regarded
as the vestments, or the voices, of the unseen combatants. Life was at