70 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVI.) 
consequence of the excellent conducting power of the solution used ; but they do not 
oucur if care be taken to avoid any disturbance of the plates or the solution, and 
then, as before said, the whole acquires a normal and perfectly inactive state. 
1829. Here then is an arrangement in which the contact of platinum and iron at x 
is at liberty to produce any effect which such a contact may have the power of pro- 
ducing ; and yet what is the consequence ? absolutely nothing. This is not because 
the electrolyte is so bad a conductor that a current of contact cannot pass, for cur- 
rents far feebler than this is assumed to be, pass readily (1813.) ; and the electrolyte 
employed is vastly superior in conducting power to those which are commonly used 
in voltaic batteries or circles, in which the current is still assumed to be dependent 
upon contact. The simple conclusion to which the experiment should lead is, in my 
opinion, that the contact of iron and platinum is absolutely without any electro- 
motive force (1835. 1859. 1889.). 
1830. If the contact be made really active and effective, according to the beautiful 
discovery of Seebeck, by making its temperature different to that of the other parts 
of the circuit, then its power of generating a current is shown (1824.). This enables 
us to compare the supposed power of the mere contact with that of a thermo con- 
tact ; and we find that the latter comes out as infinitely greater than the former, for 
the former is nothing. The same comparison of mere contact and thermo contact 
maybe made by contrasting the effect of the contact c at common temperatures, with 
either the contact at a or at b, either heated or cooled. Very moderate changes of 
temperature at these places produce instantly the corresponding current, but the 
mere contact at x does nothing. 
1831. So also I believe that a true and philosophic and even rigid comparison 
may be made at x, between the assumed effect of mere contact and that of chemical 
action. For if the metals at x be separated, and a piece of paper moistened in dilute 
acid, or a solution of salt, or if only the tongue or a wet finger be applied there, then 
a current is caused, stronger by far than the thermo-currents before produced (1830.), 
passing from the iron through the introduced acid or other active fluid to the platinum. 
This is a case of current from chemical action without any metallic contact in the 
circuit on which the effect can for a moment be supposed to depend (879.) ; it is 
even a case where metallic contact is changed for chemical action, with the result, 
that where contact is found to be quite ineffectual, chemical action is very energetic 
in producing a current. 
1832. It is of course quite unnecessary to say that the same experimental compa- 
risons may be made at either of the other contacts, a or b. 
1833. Admitting for the moment that the arrangement proves that the contact of 
platinum and iron at x has no electromotive force (1835. 1859.), then it follows also 
that the contact of either platinum or iron with any other metal has no such force. 
For if another metal, as zinc, be interposed between the iron and platinum atx, fig. 2, 
