Text: The great fundamental problem which Faraday called up anew for discussion was the existence of forces working directly at a distance without any intervening medium. During the last and the beginning of the present century, the model after the likeness of which nearly all physical theories were formed was the force of gravitation acting between the sun, the planets, and their satellites. It is know with how much caution and even reluctance Sir Isaac Newton himself proposed his grand hypothesis, which was destined to become the first great and imposing example of the power of true scientific method. We need not wonder that Newton's successors attempted at first to gain the same success by introducing analogous assumptions into all the various branches of natural philosophy. Electrostatic and magnetic phenomena especially appeared as near relations to gravitation, because electric and magnetic attractions and repulsion, according to Coulomb's measurements, diminish in the same proportion as gravity with increasing distance. But then came Oersted's discovery of the motions of magnets under the influence of electric currents. The force acting in these phenomena had a new and very singular character. It seemed as if this force would drive a single isolated pole of magnet in a circle around the wire conducting the current, on and on, without and end, never coming to rest. And although it is not possible really to separate one pole of a magnet from the other, Ampère succeeded in producing such continuous circular motions by making a part of the current itself movable with the magnet. This was the starting point for Faraday's researches on electricity. He saw that a motion of this kind could not be produced by any force of attraction or repulsion, working from point to point. The first motive which guided him seems to have been an instinctive [conception] of the law of conservation of energy, which many attentive observers of nature had entertained before it was brought by Joule to a precise scientific definition. If the current is able to increase the velocity of the magnet, the magnet must react on the current. So he made the experiment and discovered induced currents. He traced them out through all the various conditions under which they ought to appear. He found that an electromotive force striving to produce these currents arises wherever and whenever magnetic force is generated or destroyed. He concluded that in part of space traversed by magnetic force there ought to exist a peculiar state of tension and that every change of this tension produces electromotive force. This unknown hypothetical state he called provisionally the electronic state, and he was occupied for years and years in finding out what this electronic state was: He first discovered in 1838 the dielectric polarization of electric insulators subject to electric forces. Such bodies, under the influence of electric forces, exhibit phenomena perfectly analogous to those observed in soft iron under the influence of the magnetic forces. Eleven years later, in 1849, he was able to demonstrate that all ponderable matter is magnetized under the influence of sufficiently intense magnetic forces, and at the same time he discovered the phenomena of diamagnetism, which indicated that even space, devoid of all ponderable matter, is magnetizable. The most simple explanation of these phenomena, indeed, is that diamagnetic bodies are less magnetizable than a vacuous space or than the luminiferous ether filling that space. In this way real changes corresponding to that hypothetical electronic state were demonstrated. And now, with quite a wonderful sagacity and intellectual precision, Faraday performed in his brain the work of a great mathematician without using a single mathematical formula. He saw with his mind's eye that magnetized and dielectric bodies ought to have a tendency to contract in the direction of the lines of force and to dilate in all direction perpendicular to the former, and that by these systems of tensions and pressures -- in the space which surrounds electrified bodies, magnets, or wires conducting currents -- all the phenomena of electrostatic, magnetic, and electromagnetic attraction, repulsion, and induction could be explained without recurring at all to forces acting directly at a distance. This was part of his path where so few could follow him. Perhaps a Clerk Maxwell, a second man of the same power and independence of intellect, was needed to reconstruct in the normal methods the science the great building, the plan of which Faraday had conceived in his mind and attempted to make visible to his contemporaries. Nobody can deny that this new theory of electricity and magnetism, originated by Faraday and developed by Maxwell, is in itself consistent, is in perfect and exact harmony with all the known facts of experience, and does not contradict any one of the general axioms of dynamics, which have been hitherto considered the fundamental truths of all natural science because they have been found valid, without any exception, in all known processes of nature. A confirmation of great importance was given to this theory by the circumstances, demonstrated by Clerk Maxwell, that the qualities which it must attribute to the imponderable medium filling space are able to produce and sustain magnetic and electric oscillations, propagating like waves and with a velocity exactly equal to that of light. Several parts even of the theory of light are deduced with less difficulty from this new theory than from the well-known undulatory theory of Huygens, which ascribes to the luminiferous ether the qualities of a rigid elastic body. Nevertheless, the adherents of direct action at a distance have not yet ceased to search for solutions of the electromagnetic problem. The motive forces exerted upon each other by two wires conducting galvanic currents had long ago been reduced in a very ingenious way, by Ampère, to attracting or repelling forces belonging to the linear elements of every current. The intensity of these forces is considered to depend, not only on the distance of both parts of the current, but also in a rather complicated manner on the angles which the directions of the two currents make with each other and with the straight line joining them both. Ampère was not acquainted with induced currents, but phenomena of these could be derived from the law of Ampère, connecting it with the general law, deduced by Faraday from his experiments, that the current induced by the motion of a magnet or of another current always resists this motion. The general mathematical expression of this law was established by Professor Neumann, of Konigsberg. It gave directly, not the value of the forces, but the value of their mechanical work, the value of what mathematicians call an electrodynamic potential; and it reduced electromagnetic phenomena to forces acting, not from point to point, but from one linear element of a current to another. Linear elements of a wire conducting a galvanic current are, of course, complicated structures compared with atoms. I have myself elaborated several mathematical papers to prove that this formula of Professor Neumann was in harmony with all the known phenomena exhibited by closed galvanic circuits and that it did not come into contradiction with the general axioms of mechanics in any case of electric motion. I succeeded in finding an experimental method of observing electrostatic effects of electromagnetic induction under conditions in which closed circuits could not be generated. This experiment decided against the supposition that Neumann's theory was complete so long as only the electric motions in metallic or fluid conductors were considered as active currents, but it was in accordance with the theory of Faraday and Maxwell, who supposed that from the extremities of conducting bodies, where an electric charge collects, electric motion is continued through the insulating media separating them. Other eminent men have tried to reduce electromagnetic phenomena to forces acting directly between distant quantities of the hypothetical electric fluids, with an intensity which depends not only on the distance but also on the velocities and accelerations of those electric quantities. Such theories have been proposed by Professor W. Weber, of Gottingen, by Riemann, the too early deceased mathematician, and by Professor Clausius, of Bonn. All these theories explain very satisfactorily the phenomena of closed galvanic current. But applied to other electric motions, they all come into contradiction with the general axioms of dynamics.

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