Page:Scientific Monthly, volume 14.djvu/559

 conditions in the insulating medium surrounding the conductors concerned. A charged conductor was only one limiting boundary of an electrical field. A charge could not penetrate into a conductor, because the state of strain which was the essential condition of induction could not exist in conductors. In order for this state of strain to exist the bounding surfaces of the strained medium must be on different conductors insulated from each other, because from this theory the different surfaces must support equal and opposite stresses, and this is impossible over a conducting surface, which from its nature cannot support an electric stress at all. If the two surfaces of the region of strain, which Faraday called the dielectric, are joined by a conductor, the strain is relieved and the electrification disappears. Hence there can be no electrification upon the inner walls of a closed hollow conductor, since this would involve a condition of equal and opposite strains resting upon the same conducting surface.

It will be seen from the above that Faraday's theory does not involve the existence of any electric fluid whatever. Faraday calls attention to this in a foot-note to his Article 1298. He says:

Even in the production of a current Faraday does not admit the necessity for the passage of any electric fluid through the conductor. From his point of view, since charging a body consists in setting up a certain condition of strain in the dielectric between it and another body, or other bodies, so discharging an electrified body consists merely in removing this state of strain in the dielectric around it. This strain can exist permanently in an insulator; it breaks down rapidly in a conductor. While it is breaking down the current is said to be passing through the conductor.

Faraday's notion as to the nature of the condition which he called induction was not clear, as may be shown by the following quotation from Article 1298:

Induction seems to consist in a certain polarized state of the particles, into which they are thrown by the electrified body sustaining the action, the particles assuming positive or negative points or parts, which are symmetrically arranged with reference to each other and the inducting surfaces or particles. The state must be a forced one, for it is originated and sustained only by force, and sinks to the normal or quiescent state when the force is removed. It can be continued only in insulators by the same portion of electricity, because they only can retain this state of the particles.

When a Leyden jar is charged, the particles of the glass are forced into this polarized and constrained condition by the electricity of the charging