RECENT PROGRESS IN PHYSICS. 397 



12tli and 13th series of his Experimental researches, (Pog. Ann. 

 XLVII, XLVIII,) to support his theory of induction by a consideration 

 of the different forms of electric discharge. Pie classifies the different 

 kinds of discharge by dividing them into conductive discharge, electro- 

 lytic discharge, disruptive discharge, (sparks, brushes, &c.,) and cow- 

 vective discharge. 



•In considering the conductive discharge, Faraday endeavors to prove 

 that the difference between insulators and conductors is only quantita- 

 tive — a truth which no one, to my knowledge, has disputed.^ 



The electrolytic discharge, says Faraday, is preceded by an inductive 

 action through the electrolyte ; the inductive state being, in fact, a 

 necessary preliminary to discharge, decomposition is preceded by the 

 state of polarization or tension of tte particles of the fluid to be de- 

 composed. To this also nothing is to be objected. 



For the disruptive discharge, Faraday, in like manner, endeavors 

 to prove that the particles of the dielectric through which the discharge 

 takes place, whether in the form of a spark or brush, are also in a state 

 of tension or polarization. 



Though we cannot get a clear conception of such a state of tension 

 or polarization of the particles of air which precedes the spark or brush 

 discharge, yet the existence of such a state is not in the least doubtful, 

 neither is its admission at all opposed to the heretofore acknowledged 

 electrical theories. But Faraday goes further : he regards this polar- 

 ized state as a proof that the electric inductive effect which takes place 

 through the air, or the dielectric substituted for it, is produced by 

 means of their polarized state. For the correctness of this view Fara- 

 day has yet to furnish the proof. 



With the design of establishing his theory of induction, Faraday 

 made many experiments on sparks and brushes, which, though they 

 are not very important to the present subject, yet are interesting, and, 

 as valuable facts, will be described in another place. 



Since conduction and insulation have only a quantitative difference, 

 Faraday thinks that even in the better conducting fluids a convective 

 discharge might take place, if only a sufficient quantity of electricity 

 were present. The following experiment would seem to support this 

 opinion : 



Two platinum wires, forming the poles of a powerful voltaic bat- 

 tery, were fused hermetically, near to each other and side by side, in 

 a strong glass tube containing distilled water, having a few filaments 

 in it. When the bubbles at the electrodes, in consequence of the in- 

 creased pressure caused by the continuous development of gas, had 

 become so small that they produced only a weak ascending current, 

 • it could be noticed that the filaments were attracted and repelled be- 

 tween the two wires, as though between two oppositely charged sur- 

 faces in air or oil of turpentine. They moved so rapidly that they 

 displaced and disturbed the bubbles and the currents formed by them. 

 Faraday supposed it could hardly be doubted that, under similar cir- 

 cumstances, with a large quantity of electricity, of sufficient tension, 

 convective currents might be formed. The attractions and repulsions 

 ■ of the filaments were in fact the elements of such currents; hence_, 

 water, although it is almost an infinitely better conductor than air or 

 oil of turpentine, is a medium in which similar currents can take place. 



