phenomena, instead of being conditioned by the caprices of the
gods, are ruled by invariable laws.

Such revolutions are fittingly spoken of as evolution, on account
of their slowness. But there are others which, although of the
same order, deserve the name of revolution by reason of their
rapidity: we may instance the theories of Darwin,
overthrowing the whole science of biology in a few years; the
discoveries of Pasteur, which revolutionised medicine during the
lifetime of their author; and the theory of the dissociation of
matter, proving that the atom, formerly supposed to be eternal,
is not immune from the laws which condemn all the elements of the
universe to decline and perish.

These scientific revolutions in the domain of ideas are purely
intellectual. Our sentiments and beliefs do not affect them.
Men submit to them without discussing them. Their results being
controllable by experience, they escape all criticism.


3. Political Revolutions.


Beneath and very remote from these scientific revolutions, which
generate the progress of civilisations, are the religious and
political revolutions, which have no kinship with them. While
scientific revolutions derive solely from rational elements,
political and religious beliefs are sustained almost exclusively
by affective and mystic factors. Reason plays only a feeble part
in their genesis.