112 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XII.) 



the middle of a room, induction takes place between it and the walls of the room, 

 across the dielectric, air ; and the lines of inductive force accumulate upon the end 

 in greater quantity than elsewhere, or the particles of air at the end of the rod are 

 more highly polarized than those at any other part of the rod, for the reasons al- 

 ready given (1374.). The particles of air situated in sections across these lines of 

 force are least polarized in sections towards the walls, and most polarized in those 

 nearer to the end of the wires (1369.) : thus, it may well happen, that a particle 

 at the end of the wire is at a tension that will immediately terminate in dis- 

 charge, whilst in those even only a few inches off, the tension is still beneath that 

 point. But suppose the rod to be charged positively, a particle of air A, fig. 4. 

 next it, being polarized, and having of course its negative force directed towards the 

 rod and its positive force outwards ; the instant that discharge takes place between 

 the positive force of the particle of the rod opposite the air and the negative force of 

 the particle of air towards the rod, the whole particle of air becomes positively 

 electrified ; and when, the next instant, the discharged part of the rod resumes its 

 positive state, by conduction from the surface of metal behind, it not only acts on 

 the particles beyond A, by throwing A into a polarized state again, but A itself, be- 

 cause of its charged state, exerts a distinct inductive act towards these further par- 

 ticles, and the tension is consequently so much exalted between A and B, that dis- 

 charge takes place there also, as well as again between the metal and A. 



1435. In addition to this effect, it has been shown, that, the act of discharge 

 having once commenced, the whole operation, like a case of unstable equilibrium, is 

 hastened to a conclusion (1370. 1418.), the rest of the act being facilitated in its oc- 

 currence, and other electricity than that which caused the first necessary tension hur- 

 rying to the spot. When, therefore, disruptive discharge has once commenced at the 

 root of a brush, the electric force which has been accumulating in the conductor 

 attached to the rod, finds a more ready discharge there than elsewhere, and will at 

 once follow the course marked out as it were for it, thus leaving the conductor in 

 a partially discharged state, and the air about the end of the wire in a charged con- 

 dition ; and the time necessary for restoring the full charge of the conductor, and the 

 dispersion of the charged air in a greater or smaller degree, by the joint forces of re- 

 pulsion from the conductor and attraction towards the walls of the room, to which 

 its inductive action is directed, is just that time which forms the interval between 

 brush and brush (1420. 1427. 1431.). 



1436. The words of this description are long, but there is nothing in the act or the 

 forces on which it depends to prevent its being instantaneous, as far as we can estimate 

 and measure it. The consideration of time is, however, important in several points 

 of view (1418.), and in reference to disruptive discharge, it seemed from theory 

 far more probable that it might be detected in a brush than in a spark, for in a brush, 

 the particles in the line through which the discharge passes are in very different 

 states as to intensity, and the discharge is already complete in its act at the root of 



