Dr. Hare's Second Letter to Prof. Faraday. 475 



sing electrometer, the plate of air interposed between the discs 

 is, 1 believe, universally admitted to perform the part of an 

 electric, and to be equivalent in its properties to the glass in 

 a coated pane. 



67. When I adverted to a gradual relinquishment of elec- 

 tricity by the air to the glass, I did not mean to suggest that 

 it was attended by any more delay than the case actually de- 

 monstrates. It might be slow or gradual, compared with the 

 velocity of an electric discharge, and yet be extremely quick 

 comparatively with any velocity ever produced in ponderable 

 matter. That the return should be slow when no coating 

 was employed, and yet quick when it was employed, as stated 

 by you (38), is precisely what I should have expected, because 

 the coating only operates to remove all obstruction to the 

 electric equilibrium. The quantity or intensity of the excite- 

 ment is dependent altogether upon the electrified surfaces of 

 the air and the glass. You have cited (16f52) the property of 

 a charged Leyden jar, as usually accoutred, of electrifying a 

 carrier ball. This I think sanctions the existence of a power 

 to electrify, by convection, the surrounding air to a greater or 

 less depth; since it must be evident that every aerial particle 

 must be competent to perform the part of the carrier ball. 



68. Agreeably to the Franklinian doctrine, the electricity 

 directly accumulated upon one side of a pane repels that upon 

 the other side. You admit that this would take place were a 

 vacuum to intervene; but when ponderable matter is intei'- 

 posed you conceive each particle to act as does the body B, 

 when situated as described between A and C (4). But agree- 

 ably to the view which I have taken, and what I understand 

 to be your own exposition of the case, B is altogether passive, 

 so that it cannot help, if it does not impede, the repulsive 

 influence. Moreover, it must be quite evident, that were B 

 removed, and A approximated to C, without attaining the 

 striking distance, the effect upon C, and the consequent energy 

 of any discharge upon it from A, would be greater instead of 

 less. If, in the charge of a coated pane, the intermediate 

 ponderable vitreous particles have any tendency to enhance 

 the charge, how happens it that, the power of the machine 

 employed being the same, the intensity of the charge which 

 can be given to an electric is greater in proportion to its 

 tenuity? 



69. In reference to the direction of any discharge, it appears 

 to me that as, in charging, the fluid must always pass from the 

 cathode to the anode, so in reversing the process it must pur- 

 sue the opposite course of going from the anode back to the 

 cathode. Evidently the circumvolutions of the circuit are as 



