Will it be possible to maintain these equations? I am not thinking here of the comparatively slight modifications that have been found necessary in the theory of relativity; and by which we explain, for instance, the curvature of a ray of light in a gravitation field. A greater and really serious danger is threatening from the side of the quantum theory, for the existence of amounts of energy that remain concentrated in small spaces during their propagation, to which several phenomena seem to point, is in absolute contradiction to Maxwell's equations. However this may be, even if further development should require profound alterations, Maxwell's theory will always remain a step of the highest importance in the progress of physics. But I must not trespass any longer on your patience. Let me rather thank you for the attention with which you have listened to what I had to say, which was mainly intended as a tribute to the memory of one of the greatest Masters of Science.