The first of the three points we have called attention to has, so to speak, become famous through the lectures of du Bois-Reymond, which attracted much attention, on “The Limits of Natural Knowledge,” and “The Seven Riddles of the Universe.” That these thoughtful lectures made so great an impression did not mean that a great new discovery had been made, but was rather a sign of the general lack of reflection on the part of the public, for they only expressed what had always been self-evident, and what had only been forgotten through thoughtlessness, or concealed by polemical rhetoric. Consciousness, thought, even the commonest sensation of pleasure and pain, or the simplest sense-perception, cannot be compared with “matter and energy,” with the movements of masses. They represent a foreign and altogether inexplicable guest in this world of matter, molecules, and elements. Even if we could follow the play of the nervous processes with which sensation, consciousness, pain, or pleasure are bound up, into their most intricate and delicate details, if we could make the brain transparent, and enlarge its cells to the size of houses, so that, with searching glance, we could count and observe all the processes, and even follow the dance of the molecules within it, we should never see “pain,” “pleasure,” or “thought,” or anything more than bodies and their movements. A thought, such as, for instance, the perception that two and two make four, is not long or broad, above or beneath; it cannot be measured or weighed in inches or pounds like matter, tested with the manometer, thermometer, or electrometer for its potential or intensity and tension, measured by ampères or volts or horse-powers like energies and electric currents; it is something wholly different, which can be known only through inner experience, but which is much better known than anything else whatever, and which it is absolutely impossible to compare with anything but itself. Even if we admit that it can only become actual and develop as an accompaniment of processes within bodies, and only within those bodies we call “living,” and that wherever bodies exist psychical phenomena occur; even if we were able, as we never shall be able, to produce living beings artificially in a retort, and even if psychical phenomena occurred in these also, we should still have made no progress towards explaining what the psychical really is. It would still only be the blazing up in these bodies of a flame which, in some inexplicable way, had fallen upon them, and associated itself with them. We do not doubt that this association, where it takes place, does so in obedience to the strictest law and the most inexorable necessity; therefore, that wherever and however the corporeal conditions are produced, sensation and consciousness will awaken. For we believe in a world governed by law. But the mystery is in no way lessened by this, and the modern theory of evolution throws no light into this utterly