THEORY OF CONTACT ELECTROMOTJ VE FORCE CONSIDERED. 
81 
Of these varied combinations, not one gave the least signs of a current, provided 
differences of temperature were excluded; though in every case the circle formed 
was, as to conducting power, perfect for the purpose, i. e. able to conduct even a very 
weak thermo current. 
1870. In the contact theory it is not therefore the metals alone that must be as- 
sumed to have their contact forces so balanced as to produce, in any circle of them, 
an effect amounting to nothing (1809.); but all solid bodies that are able to conduct, 
whether they be forms of carbon, or oxides, or sulphurets, must be included in the 
same category. So also must the electrolytes already referred to, namely, the solu- 
tions of suiphuret of potassium and potash, and nitrous and nitric acids, in every 
case where they do not act chemically. In fact all conductors that do not act che- 
mically in the circuit must be assumed, by the contact theory, to be in this condition, 
until a case of voltaic current without chemical action is produced (1858.). 
1871- Then, even admitting that the results obtained by Volta and his followers 
with the electrometer prove that mere contact has an electromotive force and can 
produce an effect, surely all experience with contact alone goes to show that the elec- 
tromotive forces in a circuit are always balanced. How else is it likely that the above- 
named most varied substances should be found to agree in this respect? unless indeed 
it be, as I believe, that all substances agree in this, of having no such power at all. 
If so, then where is the source of power which can account by the theory of contact 
for the current in the voltaic pile ? If they are not balanced, then where is the suf- 
ficient case of contact alone producing a current? or where are the numerical data 
which indicate that such a case can be (1808. 1868.) ? The contact philosophers are 
bound to produce, not a case where the current is infinitesimally small, for such cannot 
account for the current of the voltaic pile, and will always come within the debatable 
ground which De la Rive has so well defended, but a case and data of such dis- 
tinctness and importance as may be worthy of opposition to the numerous cases pro- 
duced by the chemical philosopher (1892.) ; for without them the contact theory as 
applied to the pile appears to me to have no support, and, as it asserts contact elec- 
tromotive force even with the balanced condition, to be almost without foundation. 
1872. To avoid these and similar conclusions, the contact theory must bend 
about in the most particular and irregular way. Thus the contact of solution of 
suiphuret of potassium with iron must be considered as balanced by the joint force 
of its contact with platinum, and the contact of iron and platinum with each other ; 
but changing the iron for lead, then the contact of the suiphuret with the latter metal 
is no longer balanced by the other two contacts, it has all of a sudden changed its re- 
lation : after a few seconds, when a film of suiphuret has been formed by the chemical 
action, then the current ceases, though the circuit be a good conductor (1885.) ; and 
MDCCCXL. M 
