It is true, the considerations I have enumerated are based upon a mere surface view of things, but the more accurate methods of science seem, at first sight, to confirm the general conclusions to which they lead. On this point, it would be well to dwell for a moment. John Stuart Mill acknowledges that "the evidence is well-nigh complete that all thought and feeling has some action of the bodily organism for its immediate coincident and accompaniment, and that the specific variations, and especially the different degrees of complication of the nervous and cerebral organism, correspond to differences in the development of our mental faculties." The prodigious difficulties in the way of the study of the brain may long retard the progress of the investigator, but for the purposes of our argument we are at liberty to assume whatever is within the limits of possible achievement. We may suppose that physiology will succeed so far that the brain will be accurately and completely mapped out, and that the motions of the atoms upon which the thousand varying modes of thought and feeling depend, will be known and measured. In anticipating such results, we have reached the utmost tenable position of materialism. But now to our surprise we discover that all this being allowed, the ultimate question, what is soul, remains still unsolved and as insoluble as ever. The unvarying coincidence of certain modes of soul with certain material processes may be within the range of proof, but what cannot be proven is, that these material processes explain the psychic phenomena. If it is urged that the same difficulty presents itself in the explanation of the most ordinary occurrences, this objection is based upon a misapprehension of the point at issue. The scientist cannot show why heat should be convertible into motion, but how it is thus transformed is easy to demonstrate, and the exact mechanical equivalent of heat has been calculated. But how certain motions of atoms in the brain should generate, not heat, but consciousness, but thought and love, is past all conception. There are here two different orders of facts, having no common principle to which they could both be reduced. There is an impassable gulf between them which can in nowise be bridged over. Nor would it avail us to endow the atom itself with the promise and potency of intellect; we should thereby throw back the issue a step further, and disguise the problem whose existence it were better to plainly acknowledge. The broad fact of consciousness therefore remains unexplained and inexplicable as before. Arrived at this limit, science itself pauses and refuses to pass further.