468 Dr. Hare*s Second Letter to Prof. Paraday. 



it, as your efforts to define it in paragraph 3 would imply. I 

 have been accustomed to restrict the use of it to the rase which 

 you distinguish as an inductive charge, illustrated by that of 

 the Leyden jar. To designate the states of the conductors of 

 a machine, I have almost always employed the words excited 

 or excitement. In my text book these words are used to 

 designate the state of glass or resin electrified by friction, while 

 that of coated surfaces, whether panes or jars, inductively 

 electrified, has been designated by the words charge or c/iarged. 

 4 8. I understood the word contiguous to imply contact, or 

 contiguity, whereas it seems that it was intended by you to 

 convey the idea of proximity. In the last-mentioned sense it 

 is not inconsistent with the idea of an action, at the distance 

 of half an inch : but by admitting the word contiguous to be 

 ill chosen, you have with great candour furnished me with an 

 apology for having mistaken your meaning. 



49. Any inductive action which does not exist at sensible 

 distances (20) you attribute to ordinary induction, considering 

 the case of induction through a vacuum as an extraordinary 

 case of induction. To me it appears that the induction must 

 be the same in both cases, and that the circumstcmccs under 

 which it acts are those which may be considered in the one 

 case as ordinary^ in the other extraordinary. Thus take the 

 case cited in your reply (8, 9, 10). Does the interposition of 

 the spheres alter the character of the inductive power in the 

 sphere A? 



50. Either the force exercised by the charge in A is like 

 that of gravitation, altogether independent of the influence of 

 intervening bodies, or, like that of light, is dependent on the 

 agency of an intervening matter. Agreeably to one doctrine, 

 the matter, by means of which luminous bodies act, operates 

 by its transmission from the luminous surface to that illumined ; 

 agreeably to another doctrine, the illuminating matter operates 

 by its undulations. If the inductive foxwr of electrified bodies 

 be not analogous to gravitation, it must be analogous to the 

 ))Ovver by which light is produced, so far as to be dependent 

 on intervening matter. But were it to resemble gravitation, 

 like that force it would be uninfluenced by intervening matter. 

 If your experiments prove that electrical induction is liable to 

 be modified by intervening matter, it is demonstrated that in 

 its mode of operating it is analogous to light, not to gravita- 

 tion. It is then proved that, agreeably to your doctrine, 

 electrical induction requires the intervention of matter; but 

 you admit that it acts across a vacuum, and, of course, acts 

 without the presence of poiiderable matter. Yet it recjuires 

 intervening matter of some kind, and since that matter is not 



