note we hear in a piece of music has its definite correlative in the mechanics of the organ, and that it is accompanied by a depression and a rising again of some particular key.  In his views thus far the whole world may agree with him; whilst when he adds so emphatically that in these views there is still involved a mystery, we shall not so much say that the world agrees with him as that he, like a good sensible man, agrees with the world.  The passage from mind to matter is, Dr. Tyndall says, unthinkable.  The common sense of mankind has always said the same.  We have here a something, not which we are doubtful how to explain, but which we cannot explain at all.  We have not to choose or halt between alternative conjectures, for there are absolutely no conjectures to halt between.  We are now, as to this point, in the same state of mind in which we have always been, only this state of mind has been revealed to us more clearly.  We are in theoretical ignorance, but we are in no practical perplexity.

The perplexity comes in with the second question; and it is here that the issue lies between the affirmation and the denial of a second and a supernatural order.  We will see, first, how this question is put and treated by Dr. Tyndall, and we will then see what his treatment comes to.  Is it true, he asks, as many physicists hold it is, ’that the physical processes are complete in themselves, and would go on just as they do if consciousness were not at all implicated,’ as an engine might go on working though it made no noise, or as a barrel-organ might go on playing even though there were no ear to listen to it?  Or do ’states of consciousness enter as links into the chain of antecedence and sequence which gives rise to bodily actions?’ Such is the question in Dr. Tyndall’s own phrases; and here, in his own phrases also, comes his answer. ‘I have no power,’ he says, ’of imagining such states interposed between the molecules of the brain, and influencing the transference of motion among the molecules.  The thing eludes all mental presentation. But,’ he adds, ’the production of consciousness by molecular motion is quite as unpresentable to the mental vision as the production of molecular motion by consciousness.  If I reject one result, I reject both.  I, however, reject neither, and thus stand in the presence of two Incomprehensibles, instead of one Incomprehensible.’

Now what does all this mean?  There is one meaning of which the words are capable, which would make them perfectly clear and coherent; but that meaning, as we shall see presently, cannot possibly be Dr. Tyndall’s.  They would be perfectly clear and coherent if he meant this by them—­that the brain was a natural instrument, in the hands of a supernatural player; but that why the instrument should be able to be played upon, and how the player should be able to play upon it, were both matters on which he could throw no light.