Faraday’s answer to the questions, “What is electricity?” and, “What is magnetism?” was, therefore, according to my understanding at that time, that they were manifestations of force; and where these manifestations exist there is electricity and there is magnetism, in the sense that there are pressures and tensions which are the result of a certain state of the space which may be called the electrical or the magnetic state. Faraday’s visions, as I found them nearly forty years ago, disclosed in his “Experimental Researches in Electricity,” went even so far as to suggest that matter itself consists of centres of force with lines of force proceeding from these centres in every direction to infinite distances, and where these lines are there is the body; in other words, every material body, like every electrical and every magnetic charge, extends to infinity by means of its lines of force; and hence all material bodies are in contact, explicitly denying the existence of ether. No mortal man ever suggested a bolder conception! And yet to-day we know that a conception regarding the structure of matter very similar to that first conceived by Faraday is rapidly gaining universal recognition, not merely as a new metaphysical speculation but as the logical and inexorable demand of experiment. But when Faraday told me all these strange things as I listened attentively on the slope of Goat Fell Mountain at Arran, I could not see anything in them except geometrical pictures and a lot of what appeared to me like pure metaphysics in the background of simple geometrical structures. Although I was sure that Faraday’s metaphysics had some definite physics back of it, I was unable to disentangle it from the hypothetical notions which I did not understand clearly. Maxwell, I thought, must have disentangled that physics, and I often thought of my Scotch friend at Arran who asked me the question: “Can you see in Faraday as far as Maxwell, the Scotchman, saw?” When I came to Berlin my head was full of Faraday’s lines of force starting at electrical and magnetic charges and winding in all sorts of shapes through space, like stream lines which start from the sources of a river and follow it in its flow toward the ocean. The physical facts and principles which Faraday discovered stood out sharply defined like the bright stars in the firmament of a clear and quiescent summer night; but the conception of the new view of attracting and repelling electric and magnetic forces, which he represented graphically by his lines of force, endowed with strange physical powers residing in pressures and tensions, left in my mind impressions which made me feel that my faith in the new doctrine was not very strong. Faith without conviction is a house built upon sand. Helmholtz said once: I know too well how often I sat staring hopelessly at his descriptions of the lines of force, their number and their tensions.