On the ExcUemenl of Foliate Plates. 257 



means wish to be understoocl as supporting the chemical expla- 

 nation which has been opposed to it. I am aware that it is, 

 in its turn, liable to some objections. Nevertheless it appears 

 to me that a decomposable tluid (moisture at least) is always 

 present during excitement of the pile, and that chemical ac- 

 tion is in some way essential to it. In what manner the de- 

 composable fluid acts in producing excitement, I think still a 

 question ; and on this account I have observed that all the opi- 

 nions which have l)een proposed to account for the excitement 

 of the Galvanic pile, the Galvanic trough, or the electric column, 

 are extremely unsatisfactory. 



Having laid particular stress on the fact that the contact and 

 separation of dissimilar metals occasion them to assume different 

 electrical states, that the difference is not observable while the 

 bodies are in contact, but becomes evident on their separation ; 

 and having also stated that excitement is not produced by the 

 contact and separation of plates of similar metal ; and further, 

 that the law is, as far as experiment has gone, general, and not 

 confined to metallic bodies'^, — I ventured to remark in a second 

 paperf on the subject of electricity, that the contact and sepa- 

 ration of successive particles must take place during friction; and 

 therefore, that if the phenomena of electri«.ity, as produced by 

 friction, could be consistently ex|)lained on the principles which 

 apply to the excitement of bodies by contact and separation, 

 then there would be a fair ground for generalization. By at- 

 tempting such an explanation I endeavoured to establish as a 

 position, that the contact and separation of dissimilar bodies is a 

 cause of electrical excitement, and that the excitement by fric- 

 tion is refera!>le to tiiis property. I did not, however, attempt 

 to carry the generalization fiiither: the cause of excitement of 

 the Galvanic pile I do not consider to be yet known, wherefore 

 it must be impossible to ascertain what relation it bears to the 

 cause of excitement by contact and separation. In the rapid 

 progress of investigation it will no doubt be discovered that the 

 two causes of excitement, contact and sepaiation, and combina- 

 tion (if I may so ex])ress the means of exciting the pile), are both 

 referable to <me cause, and then tiie generalization will be per- 

 fect as far as relates to the facts which at present constitute 

 electrical science. Thus, as knowledge accumulates and reason 

 is successfully exerted, the principles of science become less nu- 

 nieroiis and more general. 



Mr. De Luc, however, objects to the generalization I have at- 

 tempted on two grounds: — the first, the supposed inaccuracy of 

 my experiments, concerning which I shall add nothing to what 



* Phil. Journal, vol. xxix. Sec Kxpcriincnts. f Ibid. vol. \\\\. 



Vol. 48. No. 222. Ccl. Ihi6. R 1 have 



