The aversion to spiritism which Crookes met with in contemporary science was, from the standpoint of such a science, largely justified. Science, in the form in which Crookes himself conceived it, took for granted that the relationship of human consciousness to the world was that of external onlooking. Accordingly, if the scientist remained within the limits thus prescribed for consciousness, it was only consistent to refuse to make anything beyond these limits an object of scientific research. On the other hand, it says much for the courage and open mindedness of Crookes that he refused to be held back from what was for him the only possible way of extending the boundaries of science beyond the given physical world. Moreover, it was only natural that in his search for a world of a higher order than the physical he should, as a man of his time, first turn his attention to spiritistic occurrences, for spiritism, as it had come over to Europe from America in the middle of the nineteenth century, was nothing but an attempt by the onlooker-consciousness to learn something in its own way about the supersensible world. The spiritist expects the spirit to reveal itself in outwardly perceptible phenomena as if it were part of the physical world. Towards the end of his life Crookes confessed that if he were able to begin again he would prefer to study telepathic phenomena - the direct transference of thought from one person to another - rather than the purely mechanical, or so-called telekinetic, expressions of psychic forces. But although his interest was thus turning towards a more interior field of psychic investigation, he remained true to his times in still assuming that knowledge about the world, whatever it might be, could be won only by placing oneself as a mere onlooker outside the object of research. * The stream of new discoveries which followed Crookes's work justified his conviction that in cathode ray phenomena we have to do with a frontier region of physical nature. Still, the land that lies on the other side of this frontier is not the one Crookes had been looking for throughout his life. For, instead of finding the way into the land whither man's soul disappears at death, Crookes had inadvertently crossed the border into another land - a land which the twentieth-century scientist is impelled to call 'the country that is not ours'. The realm thrown open to science by Crookes's observations, which human knowledge now entered as if taking it by storm, was that of the radioactive processes of the mineral stratum of the earth. Many new and surprising properties of electricity were discovered there - yet the riddle of electricity itself, instead of coming nearer, withdrew into ever deeper obscurity.