it has any meaning, stands to be made of all other correlations of phenomena. When I strike a match on the box, I evoke the phenomena of light and heat. In scientific terms, I set up by friction a chemical action quite "discontinuous" with motion in mass, and this in turn sets up a wave-motion in the hypothetical ether (of which I can form no conception) representing light. Materialism no more "splits" on the one "rock" than on the other.[94] The one special difficulty as to consciousness is a difficulty that affects all philosophies alike: the difficulty that it is consciousness that must analyse consciousness. Neither by predicating "mind-stuff" nor by alleging "soul" is that difficulty evaded. There still remains the admitted correlation between brain-and-nerve action and thought; and that correlation is on all-fours with those of physics so-called. As the case is put by Dr John Drysdale (after reasonings to an apparently different effect), "It may be held proved in physiology that for every feeling, every thought, every volition, a correlative change takes place in the nerve matter;" and it is scientific to say with him that the phenomena of mind as a function "require no further explanation" than the conditions of those changes. When Dr Ferrier writes that "no purely physiological explanation can _explain_ the phenomena of consciousness," unless he simply means that there a psychological or logical element (not Spiritism) must enter into the explanation, he is merely stumbling in the old way over the word "explain." What is "explanation"? As Professor Pearson laboriously shows, and as Hume showed long ago, all that takes place in our explanations of physical phenomena is recognition of a routine of sense experience. The theological habit has given men a pseudo-conception of "explanation;" and though they have learned to dispense with that process in physics, they still confusedly demand it in biology and psychology. But the very men who at one time talk of "mystery" and "gulf" between matter and mind, at other times recognise that the mystery is no more and no less in one correlation than in another. Thus Tyndall, who elsewhere verbalises against "Materialism," after describing the development of the human organism from the egg, writes: "Matter I define as that mysterious thing by which all that is accomplished." Well, that is "modern Materialism" or nothing; the Materialism of Büchner and of Bradlaugh. The mere doctrinal or pragmatic expressions of single physicists count for nothing. As Bradlaugh put it in his debate with the Rev. Mr Westerby, it is the cases of Ferrier that count, not his opinions. The best observer is not the best formulator or thinker; and the art or science of logical speech is not gratuitously thrown in with either mathematical or artistic faculty. To turn the data of science into philosophy is a specialist's work.