and cause a photograph when not heated by an electric current. On the other hand, it would be as impossible for the will to originate bodily movement without the occurrence of a strictly physical process of cerebration, as it would be for light to shine in an Edison lamp which had been deprived of its carbon-burner. It may be said of this theory that it is highly speculative, not verifiable by any possible experiment, and therefore at best is but a mere guess. All which is, no doubt, perfectly true; but, on the other hand, we must remember that this theory comes to us as the only one which is logically possible, and at the same time competent to satisfy the facts alike of the outer and of the inner world. It is a speculation in the sense of not being verifiable by experiment; but it has much more value than ordinarily attaches to an unverifiable speculation, in that there is really no alternative hypothesis to be considered: if we choose to call it a guess, we must at the same time remember it is a guess where it does not appear that any other is open. Once more to quote Hobbes, who, as we have seen, was himself a remarkable instance of what he here says: 'The best prophet naturally is the best guesser; and the best guesser, he that is most versed and studied in the matters he guesses at.' In this case, therefore, the best prophet is not the physiologist, whose guess ends in materialism; nor the purely mental philosopher, whose guess ends in spiritualism; but rather the man who, being 'versed and studied' in all the facts appertaining to both sides of the matter, ends in the only alternative guess which remains open. And if that most troublesome individual, the 'plain man' of Locke, should say it seems at least opposed to common sense to suppose that there is anything in a burning candle or a rolling billiard-ball substantially the same as mind, the answer is that if he could look into my brain at this moment he would see nothing there but motion of molecules, or motion of masses; and apart from the accident of my being able to tell him so, his 'common sense' could never have divined that these motions in my brain are concerned in the genesis of my spoken thoughts. * * * * *