Since, according to Faraday, each particle of the charge on the sphere carries attached to it a definite number of filaments or lines of force, it is obvious that the rate at which the charge on the sphere increases is, as I described above, the same as the rate at which the number of these lines of force are crowded into the space surrounding the sphere. Motion of the charge to the surface of the sphere is accompanied by a motion of the Faraday lines of force through every surface which surrounds the charged sphere. Since, according to Faraday, electricity is everywhere where the lines of force are, it follows that the motion of the lines through any surface means motion of electricity (in the sense in which I use this word) through that surface. Maxwell said, according to my understanding of Helmholtz, that motion of electricity, as represented by the motion of Faraday’s lines of force, is an electrical current just as much as the motion of electrical charges is. Electrical charges are terminals, only, of the lines of force; and why should the motion of the terminals be endowed with a power which is denied to the remaining parts of the lines of force? The principal power is, according to Oerstedt’s discovery, the generation of magnetism; that is, magnetic lines of force. According to Maxwell, then, the electrical current (that is, the motion of electrical charges through conductors) does not stop at the surface of the conductor, but continues in the non-conducting space beyond as motion of Faraday’s lines of force, as _motion of electricity_. The extension of the meaning of the word electrical current, just described, was, according to Helmholtz, the cardinal difference between the old electrical theories and the Faraday-Maxwell electromagnetic theory, and Helmholtz declared in favor of the last. I applauded Helmholtz and took off my hat to his clear vision of things which other people, including myself, failed to see. But can any one blame ordinary mortals, who were always accustomed to look upon the electrical current as motion of electrical charges in conductors, when they failed to see that the electrical current can take place even in a vacuum where there are no electrical charges at all, and therefore no motion of them? That was the physical concept which found its way so slowly into minds polarized by preconceived notions even after Helmholtz’s lucid explanation. This is substantially all there is in the Faraday-Maxwell electromagnetic theory as I gathered it directly from the Helmholtz address. But there is another very important element which I ought to describe here.