of the Electric Force traversing Interposed Media. 189 



no such action could take place, the platinum poles being 

 placed in separate cups filled with water*. 



The accuracy then of Mr. Becquerel's experiments having 

 been fully established, the question arises, how are we to 

 reconcile them wiih other well-known contradictory facts? 

 such as for instance those of Sir H. Davyt, — solid potash 

 and sulphuric acid combining in an isolated platinum cruci- 

 ble, and causing no electrical development. Again, a plate 

 of copper and of sulphur, when heated, have their elec- 

 trical states increased until chemical action begins, when they 

 cease. 



The simplest and clearest course, and that most reconcile- 

 able with the laws of statical electricity, seems to me to be : — 

 to consider that no electrical development is caused by the 

 union of an alkali with an acid, (the electricity being thereby 

 disguised,) but that, at the instant before the union takes place, 

 the particles of the alkali and of the acid, being in opposite 

 electrical states, affect their surrounding particles by induc- 

 tion, causing thereby a feeble current of electricity to circulate 

 from the acid through the galvanometer to the alkali, which 

 supposition is borne out by the fact, that a dry acid and alkali, 

 when in contact, show opposite electrical states. 



The same arguments apply equally well with regard to 

 thermo-electricity. The contact of two metals produces in 

 them opposite electrical states. Their chemical union in an 

 isolated vessel gives no electrical development ; thus a " solid 

 amalgam of bismuth and lead become liquid when mixed 

 together, without producing any electrical effect:!^." Again, 

 " a thin plate of zinc placed upon a surface of mercury, and 

 separated by an insulating body, is found to be positive, the 

 mercury negative ; but when kept together a sufficiently long 

 time to amalgamate^ the compound gives no signs of elec- 

 tricityl." 



These experiments explain why the contact of the two ex- 

 tremities of metallic wires, constituting a closed circuit, should, 

 as the potash and nitric acid just mentioned, produce an in- 

 duced electric current. That the electric states of different 

 metals in contact, when excited by heat, do not follow the law 

 of their natural electrical states, and change on increase of 

 temperature, is no argument against the explanation 1 have 

 given, for upon what this change in the electrical excitation 



* He might have added anothei" experiment, free from all objections — 

 namely, the increased intensity consequent upon an increased number of 

 alternations of acid and alkali. 



t Phil. Trans. J Bali erian Lecture, 1807. 



1 Ibid. 



