I know not how much of originality or importance may be attributed by subsequent students of the subject to the step next in order in this series of approximations. To those immediately concerned, the feeling of a new departure was inevitably given by the very smallness of the support which they for a long time received, and by the difficulty which they found in making their point of view intelligible to the scientific, to the religious, or even to the spiritualistic world. In about 1873--at the crest, as one may say, of perhaps the highest wave of materialism which has ever swept over these shores--it became the conviction of a small group of Cambridge friends that the deep questions thus at issue must be fought out in a way more thorough than the champions either of religion or of materialism had yet suggested. Our attitudes of mind were in some ways different; but to myself, at least, it seemed that no adequate attempt had yet been made even to determine whether anything could be learnt as to an unseen world or no; for that if anything were knowable about such a world in such fashion that Science could adopt and maintain that knowledge, it must be discovered by no analysis of tradition, and by no manipulation of metaphysics, but simply by experiment and observation;--simply by the application to phenomena within us and around us of precisely the same methods of deliberate, dispassionate, exact inquiry which have built up our actual knowledge of the world which we can touch and see. I can hardly even now guess to how many of my readers this will seem a truism, and to how many a paradox. Truism or paradox, such a thought suggested a kind of effort, which, so far as we could discover, had never yet been made. For what seemed needful was an inquiry of quite other scope than the mere analysis of historical documents, or of the _origines_ of any alleged revelation in the past. It must be an inquiry resting primarily, as all scientific inquiries in the stricter sense now must rest, upon objective facts actually observable, upon experiments which we can repeat to-day, and which we may hope to carry further to-morrow. It must be an inquiry based, to use an old term, on the uniformitarian hypothesis; on the presumption, that is to say, that _if a spiritual world exists, and if that world has at any epoch been manifest or even discoverable, then it ought to be manifest or discoverable now_.