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. BecquereFs 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. Davyf, — 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 J.” 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- 
tricityj.’* 
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 I have 
given, for upon what this change in the electrical excitation 
* He might have added another experiment, free from all objections — 
namely, the increased intensity consequent upon an increased number of 
alternations of acid and alkali. 
t Phil. Trans., Bakerian Lecture, 1807. 
X Ibid. 
