these facts is equally certain. It is, therefore, sure that all of space that is accessible to us is not void, but is filled with a substance capable of entering into vibration—the ether. But while we have clear notions of the geometrical conditions of the phenomena that occur in this matter, their physical nature is very obscure; and what we know of the properties of the substance is full of contradictions. Comparing the waves of light with those of sound, they were regarded as elastic. But only longitudinal waves have been observed in fluids, and under the conditions of matter transverse waves are impossible in them. We have been obliged, therefore, to assume that the ether acts as a solid body. But when we regard the motions of the stars and endeavor to determine their conditions, we have to affirm that ether behaves like a perfect fluid. Without endeavoring at present to explain the contradiction that presents itself here, we pass to electricity; it may throw some light on the problem.
Most of the persons who ask what electricity is have no doubts respecting its real existence, and only expect a description of the properties of the singular substance. With scientific man, the problem takes the form, Does electricity really exist? Do not electric phenomena, like the other ones, go back to properties of ether and ponderable matter? Our knowledge does not as yet permit us to answer this question affirmatively. Material electricity still has a place in our conceptions, and the old and familiar idea of two kinds attracting and repelling one another, to which are attributed actions at a distance resembling intellectual qualities, still persists in current language. This theory dated from the time when Newton's law of gravitation having been confirmed by astronomy, the idea of action at a distance without the intervention of a medium was familiar. Electric and magnetic attractions were thought to obey the same law as gravitation; and, admitting a similar action at a distance, the phenomenon was supposed to be explained in the simplest manner, and the limits of knowledge on the subject to have been reached. A different aspect was presented when in this century the reciprocal action of currents and magnets was discovered, an action infinitely variable, in which motion and time played a great part. In the necessity of increasing the number of actions at a distance to complete the theory, the simplicity which gave it its scientific probability disappeared. Simple formulas and general and elementary laws were then sought, of which Weber's law was the most important tentative. Whatever may be thought of the exactness of these essays, they formed an exceptional system and a seductive whole, a magic circle, which one could not leave after having once entered it. The road was one that could not lead to the truth. It required a fresh mind to resist the current, one
