"I am far from pretending that it may not be capable of proof, or that it is not an important addition to our knowledge, if proved, that certain motions in the particles of bodies are the _conditions_ of the production of heat or light; that certain assignable physical modifications of the nerves may be the conditions, not only of our sensations and emotions, but even of our thoughts; that certain mechanical and chemical conditions may, in the order of nature, be sufficient to determine to action the physiological laws of life. All I insist upon, in common with every thinker who entertains any clear idea of the logic of science, is, that it shall not be supposed that by proving these things, one step would be made toward a real explanation of heat, light, or sensation; or that the generic peculiarity of those phenomena can be in the least degree evaded by any such discoveries, however well established. Let it be shown, for instance, that the most complex series of physical causes and effects succeed one another in the eye and in the brain, to produce a sense of color; rays falling on the eye, refracted, converging, crossing one another, making an inverted image on the retina; and after this a motion--let it be a vibration, or a rush of nervous fluid, or whatever else you are pleased to suppose, along the optic nerve--a propagation of this motion to the brain itself, and as many more different motions as you choose; still, at the end of these motions there is something which is not motion, there is a feeling or sensation of color. The mode in which any one of the motions produces the next, may possibly be susceptible of explanation by some general law of motion; but the mode in which the last motion produces the sensation of color cannot be explained by any motion; it is the law of color, which is, and must always remain a peculiar thing. Where our consciousness recognizes between two phenomena an inherent distinction; where we are sensible of a difference, which is not merely of degree; and feel that no adding one of the phenomena to itself will produce the other; any theory which attempts to bring either under the laws of the other must be false." [5] Logic, p. 548. Amer. Edition. To precisely the same effect, DuBois Reymond, in an address to the Congress of German Naturalists given in Leipsic: "It is absolutely and forever inconceivable that a number of carbon, hydrogen, nitrogen and oxygen atoms, should be otherwise than indifferent to their own position and motion, past, present, or future. It is utterly inconceivable how consciousness should result from their joint action."