12 Second Letter from Dr. Hare to Prof. Faraday. 



When I adverted to a gradual relinquishment of electricity 

 by the air to the glass, I did not mean to suggest that it was at- 

 tended by any more delay than the case actually demonstrates. 

 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, (xxxviii,) is pre- 

 cisely what I should have expected ; because the coating only 

 operates to remove all obstruction to the electric equilibrium. 

 The quantity or intensity of the excitement is dependent alto- 

 gether upon the electrified surfaces of the air and the glass. 

 You have cited (1632,) the property of a charged Leyden jar, as 

 usually accoutered, 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. 



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 interposed, you con- 

 ceive each particle to act as does the body B when situated as 

 described between A and C, (iv.) But agreeably to the view 

 which I have taken, and what I understand to be your own ex- 

 position 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 ma- 

 chine employed being the same, the intensity of the charge which 

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



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 pursue, as I have 

 alleged, the opposite course of going from the anode back to the 

 cathode. Evidently the circumvolutions of the circuit are as un- 



