now speaking of is a merely fanciful idea; but to these I will not make any reply --- the matter is one requiring careful development, and a partial and inadequate explanation would be worse than useless. I must therefore leave its discussion to some other occasion and in the meanwhile ask my readers to assume the existence of this Force simply as a working hypothesis. In asking this I am not asking more than they are ready to concede in the case of physical science, where it is necessary to assume the existence of purely speculative conditions of energy and matter if we would co-ordinate the observed phenomena of Nature into an intelligible whole; and in like manner I would ask the critical reader to assume as a working hypothesis the existence of an Essence intermediate between the Originating Spirit and the world of external manifestation.

The existence of such an intermediary is a conclusion which has been arrived at by some of the deepest thinkers who have ever lived, and it has been called by various names in different countries and ages; but for the purpose of the present book I think I cannot do better than adopt the name given to it by the European writers of the fifteenth, sixteenth, and seventeenth centuries. They called it "Anima Mundi", or the Soul of the World, as distinguished from "Animus Dei", or the Divine Spirit, and they were careful to discriminate between the two.