Dr. Faraday on the Chemical and Contact Theories. 477 
cannot doubt, they are found to be nearly correct, to promul- 
gate as much as possible the facts, in order that so valuable 
a material may be speedily appreciated by the British agri- 
culturist. 
In conclusion I have to add, that these experiments were 
not originally commenced with that attention to rigid accu- 
racy which is called for in strictly scientific investigations, 
for they were in fact intended to serve as illustrations to a 
course of practical lectures on the application of science to 
agriculture delivered on the spot, and this may form some 
excuse for the omission of certain data which could easily 
have been obtained, but which did not appear necessary until 
it was decided to calculate and exhibit the results in a tabular 
form. 
LXXXI. On the Chemical and Contact Theories of the Voltaic 
Battery. By Micuaet Farapay, D.C.L., F.R.S., &¢.* 
[ According to our intention expressed at page 269, we now reprint 
Dr. Faraday’s argument against the contact theory of excite- 
ment in the voltaic battery, drawn from the consideration of the 
general and invariable laws of natural forces.—Ep. ] 
Improbable Nature of the Assumed Contact Force. 
2065. I HAVE thus given a certain body of experimental 
evidence and consequent conclusions, which seem to 
me fitted to assist in the elucidation of the disputed point, in 
addition to the statements and arguments of the great men who 
have already advanced their results and opinions in favour of 
the chemical theory of excitement in the voltaic pile, and against 
that of contact. 1 will conclude by adducing a further argument 
founded upon the, to me, unphilosophical nature of the force 
to which the phaznomena are, by the contact theory, re- 
ferred. 
2066. It is assumed by. the theory (1802.) that where two 
dissimilar metals (or rather bodies) touch, the dissimilar parti- 
cles act on each other, and induce opposite states. I do not 
deny this, but on the contrary think, thatin many cases such an 
effect takes place between contiguous particles; as for instance, 
preparatory to action in common chemical phenomena, and 
also preparatory to that act of chemical combination which, 
in the voltaic circuit, causes the current (1738. 1743.). 
2067. But the contact theory assumes that these particles, 
which have thus by their mutual action acquired opposite elec- 
trical states, can discharge these states one to the other, and 
yet remain in the state they were first in, being a every point 
entirely unchanged by what has previously taken place. It as- 
* From the Phil. Trans, for 1840, p, 124. 
