M.: The following case may be conceived. A certain man, X, might suddenly appear, who has control of a certain natural force that has never before been investigated; like one who knew how to use electricity at a time when people had never experienced any electrical phenomenon. He would be able to give hundreds of demonstrations, all of which we should relegate to the realm of inexplicable magic. We should, for instance, be much astonished if he were to draw sparks from a living person. Now, suppose two professors express an opinion. Professor A declares the whole thing to be a farce, and refuses to look into it at all. Professor B is ready to investigate the achievements of X only if the latter subjects himself from the beginning to all the physical conditions that are to be determined beforehand. And suppose the professor arranges his conditions so that they make impossible the occurrence of electrical phenomena. If, now, all scientists were to behave like A and B, the consequences would be very depressing. For here was an important field of investigation, which is cut off owing to the distrust or obstinacy of scientists, who should have been the first to open it up. It is quite irrelevant whether X had the character of a charlatan or not, for behind his charlatanism there were facts which clamoured for investigation. EINSTEIN: The most that I can grant is that your imagined case does not lie outside the scope of possibility. Yet the chance that there is such a "natural force" hitherto undiscovered by Man, that is, one that is a "secret force" as far as we are concerned, is so vanishingly small that it may be set down as equal to impossible. I should refuse to take part in any such practices, served up in the form of sensation, for one reason that I should regret the waste of time, as there are better things to do. It is a different matter if the mood takes me to visit a variety entertainment, in order to derive amusement from such mystifications. For example, only yesterday I was in a little theatre, in which, among diverse items, a thought-reading woman was performing. She correctly guessed the numbers 61 and 59 that I had in my mind. But let no one mention this as a case of telepathic actions at a distance or wireless communication between minds, for an intermediate person, the manager, was present, and I had to whisper the numbers to him. The distance to the stage was certainly too great to allow the sound to be conveyed directly to an audible degree. Hence there must have been a different, very cunningly arranged code of signals, which eluded the notice of people in the stalls. The process consists actually in an extraordinary refinement of observation, which does not, however, seem to me any more wonderful than the training of a reckoner who extracts cubic roots mentally, or than the practised muscles of a juggler all working in unison to enable him to perform feats with twelve plates simultaneously.