122 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVII.) 
action as that which has been given (1878. 2052.); with so many current circuits 
without metallic contact ( 201 7 .) and so many non-current circuits with (1867.) ; what 
reason can there be for referring the effect in the joint cases where both chemical action 
and contact occur, to contact, or to anything but the chemical force alone ? Such a 
reference appears to me most unphilosophical : it is dismissing a proved and active 
cause to receive in its place one which is merely hypothetical. 
5[ ix. Thermo-electric evidence. 
2054. The phenomena presented by that most beautiful discovery of Seebeck, 
thermo-electricity, has occasionally and, also, recently been adduced in proof of the 
electromotive influence of contact amongst the metals, and suchlike solid conductors* 
(1809. 1867.). A very brief consideration is, I think, sufficient to show how little 
support these phenomena give to the theory in question. 
2055. If the contact of metals exert any exciting influence in the voltaic circuit, 
then we can hardly doubt that thermo electric currents are due to the same force ; 
i. e. to disturbance, by local temperature, of the balanced forces of the different con- 
tacts in a metallic or similar circuit. Those who quote thermo effects as proofs of 
the effect of contact must, of course, admit this opinion. 
2056. Admitting contact force, we may then assume that heat either increases or 
diminishes the electromotive force of contact. For if in fig. 16. A be antimony and 
B bismuth, heat applied at x causes a current to pass in the direction of the arrow ; 
if it be assumed that bismuth in contact with antimony tends to become positive and 
the antimony negative, then heat diminishes the effect ; but if it be supposed that the 
tendency of bismuth is to become negative, and of antimony positive, then heat in- 
creases the effect. How we are to decide which of these two views is the one to be 
adopted, does not seem to me clear ; for nothing in the thermo-electric phenomena 
alone can settle the point by the galvanometer. 
2057- If for that purpose we go to the voltaic circuit, there the situation of anti- 
mony and bismuth varies according as one or another fluid conductor is used (2012.). 
Antimony, being negative to bismuth with the acids, is positive to it with an alkali 
or sulphuret of potassium ; still we find they come nearly together in the midst of the 
metallic series. In the thermo series, on the contrary, their position is at the extremes , 
being as different or as much opposed to each other as they can be. This difference 
was long ago pointed out by Professor Gumming - f : how is it consistent with the con- 
tact theory of the voltaic pile ? 
2058. Again, if silver and antimony form a thermo circle (fig. 17.), and the junc- 
tion x be heated, the current there is from the silver to the antimony. If silver and 
bismuth form a thermo series (fig. 18.), and the junction x be heated, the current is 
from the bismuth to the silver ; and assuming that heat increases the force of con- 
* See Fechner’s words, Philosophical Magazine, 1838, xiii. p. 206. 
f Annals of Philosophy, 1823, vi. 177. 
