86 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVI.) 
resisted (1861. 1865. 1872.), namely, that the solution may class with metals and such- 
like bodies, giving 1 balanced effects of contact in relation to some of these bodies, as 
in this case, to the sulphuret of lead produced, but not with others , as the lead itself ; 
both the lead and its sulphuret being in the same category as the metals generally 
(1809. 1870.). 
1889. The utter improbability of this as a natural effect, and the absence of all 
experimental proof in support of it, have been already stated (1861. 1871.)? but one or 
two additional reasons against it now arise. The state of things may perhaps be made 
clearer by a diagram or two, in which assumed contact forces may be assigned, in 
the absence of all experimental expression, without injury to the reasoning. Let fig. 4. 
Plate III. represent the electromotive forces of a circle of platinum, iron, and solution 
of sulphuret of potassium ; or platinum, nickel, and solution of sulphuret ; cases in 
which the forces are, according to the contact theory, balanced (I860.). Then fig. 5 
may represent the circle of platinum, lead, and solution of sulphuret, which does pro- 
duce a current, and, as I have assumed, with a resulting force of 11 -> . This 
in a few minutes becomes quiescent, i. e. the current ceases, and fig. 6 may represent 
this new case according to the contact theory. Now is it at all likely that by the in- 
tervention of sulphuret of lead at the contact c, fig. 5, and the production of two con- 
tacts d and e, fig. 6, such an enormous change of the contact force suffering alteration 
should be made as from 10 to 21 ? the intervention of the same sulphuret either at a 
or b (1834. 1840.) being able to do nothing of the kind, for the sum of the force of the 
two new contacts is in that case exactly equal to the force of the contact which they 
replace, as is proved by such interposition making no change in the effects of the 
circle (1867- 1840.). If therefore the intervention of this body between lead and pla- 
tinum at a , or between solution of sulphuret of potassium and platinum at b (fig. 5.) 
causes no change, these cases including its contact with both lead and the solution of 
sulphuret, is it at all probable that its intervention between these two bodies at c 
should make a difference equal to double the amount of force previously existing, or 
indeed any difference at all ? 
1890. Such an alteration as this in the sum assigned as the amount of the forces 
belonging to the sulphuret of lead by virtue of its two places of contact, is equivalent 
I think to saying that it partakes of the anomalous character already supposed to 
belong to certain fluids, namely, of sometimes giving balanced forces in circles of 
good conductors, and at other times not (1865.). 
1891. Even the metals themselves must in fact be forced into this constrained 
condition ; for the effect at a point of contact, if there be any at all , must be the re- 
sult of the joint and mutual actions of the bodies in contact. If therefore in the 
circuit, fig. 5, the contact forces are not balanced, it must be because of the deficient 
joint action of the lead and solution at c*. If the metal and fluid were to act in their 
* My numbers are assumed, and if other numbers were taken, the reasoning might be removed to contact 
b, or even to contact a, but the end of the argument would in every case be the same. 
