Thermo-Electric and Voltaic Effects     3 11
render them only a feeble voltaic combination with each other:
and with respect to silver, which stands between tin and zinc
thermo-electrically, not only must the same departure be re-
quired, but how great must the effect of this, its incongruous
contact, be, to overcome so completely as it does, and even
powerfully reverse the differences which the metals (according
to the contact theory) tend to produce!
 1049.	In further contrast with such an assumption, it must
be remembered that, though the series of thermo-electric bodies
is different from the usual voltaic order (1000), it is perfectly
consistent with itself, i.e. that if iron and antimony be weak
with each other, and bismuth be strong with iron, it will also
be strong with antimony.    Also that if the electric current pass
from bismuth to rhodium at the hot junction, and also from
rhodium to antimony at the hot junction, it will pass far more
powerfully from bismuth to antimony at the heated junction.
To be at all consistent with this simple and true relation, sul-
phuric acid should not be strongly energetic with iron or^ tin
and weakly so with silver, as it is in the voltaic circuit, since
these metals are not far apart in the therrno series:  nor should
it be nearly alike to platinum and gold voltaically, since they
are far apart in the thermo series.
 1050.	Finally, in the thermo circuit there is that relation to
heat which shows that for every portion of electric force evolved
there is a corresponding change in another force, or form of
force, namely heat, able to account for it;   this, the united
experiments of Seebeck and Peltier have shown.    But contact
force is a force which has to produce something from nothing,
a result of the contact theory which can be better stated a little
further on (1057, 1059, 1061).
 1051.	What  evidence  then  for  mere  contact  excitement,,
derivable from the facts of thermo-electricity, remains, since
the power must thus be referred to the acid or other electrolyte
used (1048) and made, not only to vary uncertainly for each
metal, but to vary also in direct conformity with the variation
of chemical action (862, 944, 980, 994, 1002)?
 1052.	The contact theorist seems to consider that the advo-
cate of the chemical theory is called upon to account for the
phenomena of thermo-electricity.    I cannot perceive that See-
beck's circle has any relation to the voltaic pile, and think that
the researches of Becquerel1 are quite sufficient to authorise,
that conclusion.
1 Annales dc Chimie, 1829, xli. 355; xlvi. 275.