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



they might be inferred to cooperate in the transmission of that 

 species of inductive influence. But if the induction takes place 

 without the ponderable matter, is it right to assume that this mat- 

 ter aids because it does not prevent the effect ? Might it not be as 

 reasonably inferred in the case of light, that although its transmis- 

 sion does not require the interposition of a pane of glass, yet that 

 when such a pane is interposed, since the light is not intercepted, 

 there is reason to suppose an active cooperation of the vitreous 

 particles in aid of the radiation ? It may be expedient here to 

 advert to the fact that Prof. Henry has found a metallic plate to 

 interfere with the dynamic induction of one flat helix upon an- 

 other. I have myself been witness of this result. 



Does not magnetic or electrodynamic induction take place 

 as well in vacuo as in pleno? Has the presence of any gas been 

 found to promote or retard that species of reaction ? It appears, 

 that agreeably to your experiments, ponderable bodies, when 

 made to intervene, did not enhance the influence, in question; 

 while in some of those performed by Henry it was intercepted 

 by them. Does it not follow that ponderable particles may im- 

 pede, but cannot assist in this process. 



I am happy to find, that among the opinions which I ex- 

 pressed in my letter to you, although there are several in which 

 you do not concur, there are some which you esteem of impor- 

 tance, though you do not consider yourself justified in extending 

 to them your sanction ; being constrained, in the present state of 

 human knowledge, to hold your judgment in suspense. For the 

 present, I shall here take leave of this subject, having already so 

 extended my letter as to occupy too much of your valuable time. 

 I am aware that as yet I have not sufficiently studied many of 

 the results of your sagacity, ingenuity, and skill in experimental 

 investigations. When I shall have time to make them the sub- 

 ject of the careful consideration which they merit, I may venture 

 to subject your patience to the additional trial resulting from some 

 further commentaries. I remain, with the highest esteem, re- 

 spectfully yours, Robert Hare. 



