We shall now, at last, come down to some special topics. What I have said hitherto may seem pretty long, if you consider it a mere introduction. But I hope it is of some interest in itself—and I could not avoid it. I had to make clear the situation. None of the new discoveries about which I may tell you is frightfully exciting in itself. What is exciting, novel, revolutionary, is the general attitude we are compelled to adopt on any attempt to synthesize them all.

Let us go in medias res. There is the problem of matter. What is matter? How are we to picture matter in our mind?

The first form of the question is ludicrous. (How should we say what matter is—or, if it comes to that, what electricity is—both being phenomena given to us once only?) The second form already betrays the whole change of attitude: matter is an image in our mind—mind is thus prior to matter (notwith-standing the strange empirical dependence of my mental processes on the physical data of a certain portion of matter, viz. my brain).

During the second half of the nineteenth century matter seemed to be the permanent thing to which we could cling.