Our modern investigators in the sciences of inorganic nature are foremost to recognize, both within and without their special fields of work, the unity of nature, the fixity of its laws, the definite sequence of cause and effect through which every fact depends on what has gone before it, and acts upon what is to come after it. They grasp firmly the Pythagorean doctrine of pervading order in the universal Kosmos. They affirm, with Aristotle, that nature is not full of incoherent episodes, like a bad tragedy. They agree with Leibnitz in what he calls 'my axiom, that nature never acts by leaps (la nature n'agit jamais par saut),' as well as in his 'great principle, commonly little employed, that nothing happens without sufficient reason.' Nor again, in studying the structure and habits of plants and animals, or in investigating the lower functions even of man, are these leading ideas unacknowledged. But when we come to talk of the higher processes of human feeling and action, of thought and language, knowledge and art, a change appears in the prevalent tone of opinion. The world at large is scarcely prepared to accept the general study of human life as a branch of natural science, and to carry out, in a large sense, the poet's injunction to 'Account for moral as for natural things.' To many educated minds there seems something presumptuous and repulsive in the view that the history of mankind is part and parcel of the history of nature, that our thoughts, wills, and actions accord with laws as definite as those which govern the motion of waves, the combination of acids and bases, and the growth of plants and animals.
The main reasons of this state of the popular judgment are not far to seek. There are many who would willingly accept a science of history if placed before them with substantial definiteness of principle and evidence, but who not unreasonably reject the systems offered to them, as falling too far short of a scientific standard. Through resistance such as this, real knowledge always sooner or later makes its way, while the habit of opposition to novelty does such