Electromotive Forces in the Voltaic Cell. 157 
Wherever electrostatic methods were employed, and where 
the electroscope was the instrument of research, contact theo- 
rists had it all their own way ; and it was only by apparent 
effort and twisting of experiments that chemical theorists 
could maintain their ground. But when electric currents 
were dealt with, and the galvanometer used, then the chemists 
had their turn, and they showed most conclusively that no 
mere contact could maintain a current unless heat disappeared 
or chemical action occurred : a fact obvious enough to us to- 
day on the principles so laboriously and finally established by 
Joule. By means of the galvanometer, the contact theory 
was so belaboured by Faraday that it ultimately seemed to 
give up the ghost, and the chemical doctrines triumphed. So 
much so, that Volta’s original fact, in spite of the evidence 
which had been accumulated, was again doubted; and one 
finds in text-books culled from this period statements that 
Volta must have had wet fingers, or that he rubbed the plates 
together, or that there was moisture in the air. Also hints 
are given that films existed on the plate, that squeezed coats 
of varnish or lacquer might produce some electricity, and so 
on. It was pointed out, moreover, by De la Rive*, how 
minute a trace of chemical action could produce how much 
electricity, and how little electrictity could affect an electro- 
scope. But it is to be noted that any chemical action caused 
by damp on the plates, or moisture in the air, would be of the 
nature of local action, and local action is not a satisfactory pro- 
ducer of manageable electricity. Sir Humphry Davy is very 
clear on this head. He shows that chemical action need pro- 
duce no electricity, instancing the burning of iron nitre on 
charcoal, potash and acid in a crucible or an electroscope, &.; 
a plate of zinc placed on mercury and separated is found posi- 
tive, but if left long enough to amalgamate, the compound 
shows no signs of electricity. Davy’s views are singularly 
advanced, and are worth quoting. 
* De la Rive: Traté @électricité, ii.p. 776 ; Annales de Chimie, xxxix. 
p. 311 (1828). 
t+ Davy, Bakerian Lecture, 1806 (see Phil. Trans. 1807, p. 39) :—“ As 
the chemical attraction between two bodies seems to be destroyed by 
giving one of them an electrical state different from that which it naturally 
possesses ..... so it may be increased by exalting its natural energy. 
Thus, while zinc is incapable of combining with oxygen when negatively 
electrified in the circuit even by a feeble power, silver easily unites to it 
when positively electrified... .. . Among the substances that combine 
chemically, all those, the electrical energies of which are well known, 
exhibit opposite electrical states... .In the present state of our knowledge 
it would be useless to attempt to speculate on the remote cause of the 
electrical energy, or the reason why diiferent bodies after being brought 
into contact should be found differently electrified ; its relation to chemi- 
cal affinity is, however, sufficiently evident. May it not be identical with 
