on certain Theoretical Opinions. 59 



ter I will employ the usual figures for the paragraphs of the 

 Experimental Researches, and small Roman numerals for 

 those of this communication. 



xx. At paragraph 3, you say, you cannot reconcile my lan- 

 guage at 1615, with that at 1165. In the latter place I 

 have said I believe ordinary induction in all cases to be an 

 action of contiguous particles, and in the former assuming a 

 very hypothetical case, that of a vacuum, I have said nothing 

 in my theory forbids that a charged particle in the centre of 

 a vacuum should act on the particle next to it, though that 

 should be half an inch off. With the meaning which I have 

 carefully attached to the word contiguous (xvi.) I see no con- 

 tradiction here in the terms used, nor any natural impossibility 

 or improbability in such an action. Nevertheless all ordinary 

 induction is to me an action of contiguous particles, being 

 particles at insensible distances : induction across a vacuum 

 is not an ordinary instance, and yet I do not perceive that it 

 cannot come under the same principles of action. 



xxi. As an illustration of my meaning, I may refer to the 

 case, parallel with mine, as to the extreme difference of in- 

 terval between the acting particles or bodies, of the modern 

 views of the radiation and conduction of heat. In radiation 

 the rays leave the hot particles and pass occasionally through 

 great distances to the next particle, fitted to receive them : in 

 conduction, where the heat passes from the hotter particles to 

 those which are contiguous and form part of the same mass, 

 still the passage is considered to be by a process precisely 

 like that of radiation ; and though the effects are, as is well 

 known, extremely different in their appearance, it cannot as 

 yet be shown that the principle of communication is not the 

 same in both. 



xxii. So on this point respecting contiguous particles and 

 induction across half an inch of vacuum, I do not see that I am 

 in contradiction with myself or with any natural law or fact. 



xxiii. Paragraph 4 is answered by the above remarks and 

 by viii. ix. x. 



xxiv. Paragraph 5 is answered according to my theory by 

 viii. ix. x. xi. xii. and xiii. 



xxv. Paragraph 6 is answered, except in the matter of 

 opinion (xviii.), according to my theory by xvi. The con- 

 duction of heat referred to in the paragraph itself will, as 

 it appears to me, bear no comparison with the phenomenon 

 of electrical induction : the first refers to the distant influence 

 of an agent which travels by a very slow process, the se- 

 cond to one where distant influence is simultaneous, so to 

 speak, with the origin of the force at the place of action : the 



