The basis of all modern Comparative Mythology, and the principle from which we start on the present studies, is that the Myth is only the expression in language of the impression made on the men of ancient time by the physical events and changes under the immediate influence of which they lived. If this is true, it cannot be questioned that the tendency and quality of the Myth must change, independently of the matter and contents which remain the same, in obedience to the advancing civilisation of men. For all progress in civilisation is marked, speaking generally, by continual development of the relation in which man stands to external nature. When a nation emerges from the stage of Nomadism and advances to an agricultural life, its relation to external nature is changed. The same thing happens when a people that lived exclusively by the chase and fishing advances to Nomadism. Since a new epoch in the development of human civilisation has commenced in our own times through the progress made in physical science, our relation to nature has again entered on a new phase. The spirit of modern civilisation has been characterised by the common-place, that reason has subdued nature. The Myth accompanied mankind from the first germ to the highest stage of mental culture, always adapting itself to man’s intellectual field of view and changing with the measure of this field of view. It is therefore a faithful mirror of the ideas of the world held by the men of each age; and these ideas are nowhere so clearly reflected as in myths. The configuration and tendency of the myths is always dependent on the ideas of men at that particular stage of civilisation which gave the myth its form and guided it to its special tendency. The traces of these historical transformations of the myths are scarcely distinguishable for small chronological divisions; but when the larger epochs of civilisation are under consideration, they cannot fail to be noted by the explorer’s eye. And the discovery and demonstration of these transformations of the tendency of the myths in their relation to the great epochs of civilisation is one of the special problems of Comparative Mythology.