We shall only be acting in the spirit of natural science if we study the spiritual development of man as impartially as the naturalist observes the sense-world. We shall then certainly be led, in the domain of spiritual life, to a kind of contemplation which differs from that of the naturalist as geology differs from pure physics and biology from chemistry. We shall be led up to higher methods, which cannot, it is true, be those of natural science, though quite conformable with the spirit of it. Such methods alone are able to bring us to the heart of spiritual developments, such as that of Christianity, or other worlds of religious conceptions. Any one applying these methods may arouse the opposition of many who believe they are thinking scientifically, but he will know himself, for all that, to be in full accord with a genuinely scientific method of thought. An investigator of this kind must also go beyond a merely historical examination of the documents relating to spiritual life. This is necessary just on account of the attitude he has acquired from his study of natural history. When a chemical law is explained, it is of small use to describe the retorts, dishes, and pincers which have led to the discovery of the law. And it is just as useless, when explaining the origin of Christianity, to ascertain the historical sources drawn upon by the Evangelist St. Luke, or those from which the "hidden revelation" of St. John is compiled. History can in this case be only the outer court to research proper. It is not by tracing the historical origin of documents that we shall discover anything about the dominant ideas in the writings of Moses or in the traditions of the Greek mystics. These documents are only the outer expression for the ideas. Nor does the naturalist who is investigating the nature of man trouble about the origin of the word "man," or the way in which it has developed in a language. He keeps to the thing, not to the word in which it finds expression. And in studying spiritual life we must likewise abide by the spirit and not by outer documents. II THE MYSTERIES AND THEIR WISDOM