Non-conducting Bodies in Electric Induction. 9 



through the sulphur and secure the resulting charge. By the 

 use of a linger key these contacts can be made in the fiftieth part 

 of a second, and by a little mechanical arrangement even much 

 quicker ; yet as far as I can find, the coated sulphur surface is as 

 fully charged in this brief period as if the induction had been 

 sustained for a minute or an hour. How are we to conceive 

 that any degree of conduction of the sulphur consistent with the 

 prolonged insulation which can follow, can have concurred to this 

 brief and complete act ? 



The foregoing results appear to me to be crucial in their cha- 

 racter, and to leave no question open as to the possibility of the 

 action of interposed insulating matter being of the same nature 

 as the action of interposed conducting matter in cases of induc- 

 tion. I would go further into them in explanation and illustra- 

 tion of my own views, and of the truthfulness of specific inductive 

 capacity, if I thought it necessary ; but I should have little more 

 to do than repeat what is already said (and that many years ago) 

 in the Eleventh Series of the Experimental Researches, and so I 

 refrain. 



The effect you mention at the bottom of page 404 and top of 

 405, Phil. Mag., is to me a very natural result of the high specific 

 inductive capacity of shell-lac. In one place you say, in relation 

 to it, that " no reason can be assigned why a small piece of shell- 

 lac," &c.; but I cannot consent to accept that as a small piece 

 which is in reality a small portion, not separated, of a large 

 piece ; as I could not say, that that was a small piece of metal 

 which is only a small part of a large plate. A greater inductive 

 capacity disturbs the lines and distribution of force in a manner 

 equivalent to a certain amount of conductive power ; and yet the 

 two effects may be perfectly distinguished by such experiments 

 and reasoning as that I have just applied to the examination of 

 the condition of the shell-lac plate. 



You will see, my dear Sir, that I am anxious to stand rightly 

 before you ; at the same time 1 would not have presumed thus 

 far if I had not believed that there was some great misapprehen- 

 sion in your mind as to my opinions. You will perceive, also, 

 that I find no reason to change any of my views of static induc- 

 tion as set forth in Series XI. I must confess, that as your paper 

 has apjjeared in Poggendorff''s Annalen and in the Philosophical 

 IMagazine, I should not like the case to remain before the scien- 

 tific world just as it is, as it might be thought I acquiesced in 

 the statements there made; and if I might suppose it would not 

 be disagreeable to you I would put this letter into the Magazine, 

 unless, indeed, you i)rcferred some other mode of communication 

 with the public. In the mean time I shall send it to you ; and 

 as many months have now elapsed since the publication here, I 



