Science has only to think about facts. There should be no distinction made between the various phenomena observed: it is not beseeming to adopt certain facts, and refuse analysis to others, excluding them on the ground, for example, that their examination belongs to religion. Every natural fact ought to be studied, and, if it be real, incorporated with the patrimony of knowledge. What matters its apparent contradiction with the laws of nature, such as we understand them to-day? These laws are not principles superior to our experience; they are but the expression of our experience: our knowledge is very limited and our experience is still young—it will grow, and its development will bring the inevitable consequence of a corresponding modification in our conception of nature. Therefore, let us not be too positive of the accuracy of present ideas, and arbitrarily reject everything which we think runs counter to them. Do not dogmatise; let our only care be the impartial search for truth. Nothing will better enable us to understand the surroundings in the midst of which we are evolving than facts, which are apparently irreconcilable with current ideas: these facts betoken that the ideas are erroneous or incomplete; their attentive observation will reveal a more general formula which will explain at one and the same time the new and the old. And thus from antithesis to synthesis, more and more universal, our scientific ideas will tend towards absolute truth. Alas! how far away from this ideal do we seem to be to-day! _Laboremus!_ CHAPTER I METHOD A French proverb says, ‘we must have eggs to make an omelette’: in order to be able to study psychical phenomena we must have psychical phenomena. This seems an elementary proposition, and yet it is the very one we most readily overlook. I have already said why and wherefore. Therefore, I deem it necessary to indicate at once the methods which have appeared to me to give the most favourable results. Those of my readers who may wish to verify the accuracy of my conclusions will, I am sure, have the opportunity of doing so, if they operate as I have done. First of all, I must warn them against caring for the world’s opinion. They must not be afraid of exposing themselves to ridicule. No doubt there is temptation to make a jest of the methods which I advise; but I strongly recommend them to think about the result, and not about the means used to obtain that result. Psychical phenomena are of two orders: material and intellectual. The methods best suited to the study of the first are not, in my opinion, adapted to the study of the second. There is a distinction, therefore, to be made in the beginning between these two categories of facts. Physical phenomena are the least frequently met with; they include:— 1. Knockings or ‘raps’ on furniture, walls, floors, or on the experimenters themselves. 2. Sundry noises other than raps.