that could enter upon, the study of the phenomena without preconceived opinions, and was capable of starting from what it observed, and not from what it had heard, read, or learned.
Faraday followed that course. He had heard that, in electrifying a body, something new was introduced into it; but he saw that the changes were external, and not within. He was told that the forces traversed space, but he remarked that the nature of the matter that filled the space had great influence on them. He had read that electricities existed, and that we only had to consider their properties; and yet he observed every day the effects of the forces without ever seeing the electricities themselves: in this way he reversed the proposition. The electric and magnetic forces became to him the only tangible reality, while electricity and magnetism fell to the rank of objects the existence of which is contestable. Considering these lines of forces, as he called them, independently of their cause, he regarded them under the form of states of space, tension, whorls, and currents, without occupying himself with what they might really be. He was satisfied with having established their existence, with observing their influence upon each other, their attractions for material bodies, and their propagation by the transmission of the excitation from one point of space to another. If it was objected that there could be no other state than absolute rest in empty space, he could answer: "Is space, then, empty? Does not the transmission of light force us to regard it as filled with matter? Can not the ether, which transmits the luminous waves, suffer modifications which we perceive under the form of electrical and magnetic actions? Is there not a relation between these modifications and these vibrations? Are not the luminous waves a kind of scintillation of these lines of force?" Such were the inductions and hypotheses which Faraday conceived. They were as yet only mental views; he applied himself earnestly to demonstrate them scientifically; and the relations of light, electricity, and magnetism became the favorite object of his studies.
The relation he found was not the one he sought. He continued his researches till age put an end to his labors. One of his principal questions was whether the transmission of electrical and magnetic forces is instantaneous. Is the magnetic field constituted at once to the limits of space whenever the current excites an electro-magnet? Or does the action first reach the nearer points and gradually propagate itself to the more remote ones? And is the sudden modification of the electric condition of a body felt simultaneously in identical variations, in all points of space, or is there a retardation augmented as the distance increases? In the latter case, the effect of the variation would be transmitted as a wave through space. Do such waves exist?