Sometimes these are merged under a common term, like the Japanese _kami_, sometimes they are separately named. They bear different characters of good and evil, as they are ready to help or hurt; and the same spirit may be now kindly and now hostile, without fixity of disposition or purpose. To such spirits the ancient Babylonians gave the name of _zi_. Literally, we are told, the word signified "life"; it was indicated in their picture-writing by a flowering plant; the great gods, and even heaven and earth themselves, all had their _zi_. The Egyptians, in like manner, ascribed to every object, to human beings, and to gods, a double or _ka_. The word seems to be identical with that for "food"; it was another way of indicating that all visible things, the peoples of the earth, the dwellers in the realms above and below, shared a common life. The history of religion is concerned with the process by which the great gods rise into clear view above the host of spirits filling the common scene; with the modes in which the forces of the world may be grouped under their control; with the manifold combinations which finally enable one supreme power to {103} absorb all the rest, so that a god of the sky, like the Greek Zeus, may become a god of rain and sunshine and atmospheric change, of earth and sea, and of the nether world; and may thus be presented as the sole and universal energy, not only of all outward things but also of the inner world of thought. Of this immense development language, archæology, literature, the dedications of worship, the testimonies of the ancient students of their still more ancient past in ritual and belief, contain the scattered witness, which the student of to-day laboriously gathers and interprets. It is the humbler object of a little manual of Comparative Religion to set some of the principal issues of such historic evolution side by side, and show how similar reactions of the mind of man upon the field of his experience have wrought like results. As the inquirer casts his eye over the manifold varieties of the world's faiths, he sees that they are always conditioned by the stage of social culture out of which they emerge. The hunter who lives by the chase, and must range over large areas for means of support; the pastoral herdsman who has acquired the art of breeding cattle and sheep, and slowly moves from one set of feeding-grounds to another; the agriculturist who has learned to rely on the co-operation of earth and sky in the annual round,--have each their own way of expressing their view of the Powers on which they depend. {104}