Mr. J.J. Waterston on some Electrical Experiments. 371 



must therefore be supplied from B, the free negative on the outer 

 side of which thus acts not only on the B side of the plate, but 

 on the A side also, to attain which it must pass round the edges 

 of the coating A. 



Faraday supposes this to take place by means of the action of 

 contiguous particles of air ; and hence it is to be presumed that it 

 is his belief that a charged pane could not exist in an illimitable 

 vacuum, or at least that the electricity on B could not affect an 

 electroscope on the side of A, because there would be no conti- 

 guous particles to transmit the force. 



This hypothesis has been supposed to be further supported by 

 the apparent augmentation in the force of induction that takes 

 place when a plate of lac or sulphur is interposed between the 

 charged body and a neighbouring conductor ; and the term specific 

 inductive capacity, applied to denote the degree of the special fa- 

 culty of transmitting the inductive power belonging to the parti- 

 cles of a given non-conducting body, seems to be now established, 

 Harris having published experiments as supporting Faraday's 

 views, and teaching them in his elementary treatise. 



As this term appears to me inapplicable to matter in rela- 

 tion to electric phenomena, I beg to submit the following experi- 

 ment as demonstrating the non-existence of such a quality. 



An insulated brass disk (the B. D. of previous experiments) 

 is suspended over the cap of the electroscope at the distance of 2 

 inches above it. A cake of sulphur, 4 inches in diameter and ^ 

 an inch thick, is provided with handles of sealing-wax projecting 

 about 10 inches from each side. It is examined to see if there 

 is any excitement upon A ; and if any, discharge is effected by 

 presenting it to a flame. The B. D. is charged from an electro - 

 phorus so that the leaves of the electroscope diverge to about 

 60°. The cake of sulphur, supported by its handles (which 

 enable the hands of the operator to be kept at such a distance 

 as not to influence the electroscope), is brought horizontally into 

 the space between the B. D. and cap of the electroscope. It is then 

 moved parallel up and down ; now close to the cap, then close to 

 B. D. When close to B. D., the leaves are not at a higher 

 angle than before its introduction; but on bringing it down 

 towards the cap the angle increases a little, and when quite 

 close to it the angle increases considerably, and this notable 

 augmentation takes place within a distance of about \ of an inch 

 from the cap. The experiment requires to be promptly per- 

 formed, because the sulphur soon becomes inductively excited in 

 the manner peculiar to non-conductors and as, to a certain degree, 

 developed in the previous experiments. On first bringing the 

 cake between the B. J), and the electroscope, the leaves descend a 

 little just as the edge cf the cake passes in between the outer 



