REPORT ON THERMO-ELECTRICITY. 805 
was common to all the metals. In the latter case it was to be 
expected that the metals might be formed into a series similar 
to the voltaic ; and if such a series were formed, that the order 
might coincide with that obtained by arranging them according 
to some of their properties previously discovered. The results 
have been so far successful as to determine the thermo-electric 
relations of the metals to each other, (subject to anomalies 
which it is not now necessary to mention,) but not to connect 
them with any other of their properties ; unless the conjecture 
of Becquerel be verified, that they are in the order of the spe¬ 
cific heats,—in which case the remark of Dr. Ritchie on gal¬ 
vanic electricity will be applicable to this branch of it, and the 
whole theory of electricity may be intimately connected with 
that of latent heat. 
The real gain to science from the knowledge of this thermo¬ 
electric series, is in the increased effect from the proper appo¬ 
sition of the metals; and as it appears that bismuth and antimony 
in conjunction, as originally proposed by Fourier and GErsted 
and myself, are the furthest removed from each other of the 
available substances, it is not probable that any single pair of 
elements will be found more efficacious. On endeavouring to 
obtain an increase of power by augmenting the number of ele¬ 
ments, it was soon discovered that this was limited by the want 
of tension in this species of electricity ; in consequence of which, 
nearly as much was lost by transmission through a number of 
elements as was gained by their united action ; and for the same 
reason the galvanometer, which had been so efficacious in mul¬ 
tiplying voltaic action, was found to be of little advantage by 
the earlier experimenters. It appears, however, that by the in¬ 
genious contrivances of Nobili and Melloni, tbis difficulty has 
been overcome, and that they have been enabled to construct a 
thermo-electric thermometer of almost incredible delicacy. If 
there be any tension in thermo-electric currents, we may hope 
that it will be detected by this instrument, in which there may 
possibly, by the transmission of the electricity through its nu¬ 
merous elements, acting as more or less perfect conductors in 
their substance and at their junctures, be induced a tension, 
similar to that in the voltaic series by the passage from metals 
to fluids. As yet the only semblance of it is that obtained by 
Fourier and CErsted in 1823 ; which was manifested by a slight 
convulsion of the muscles of a frog placed in the circuit. I am 
not aware that the experiment has been repeated ; and, with 
all due deference to such able observers, I must doubt its accu¬ 
racy. Wherever there is tension, however feeble, I should 
expect it to be attended either with the power of producing 
