302 
SECOND REPORT — 1832 . 
after reading a detail of an elaborate series of experiments, to 
discover what object was intended by them. 
The first and most obvious inquiry seems to be into the cir¬ 
cumstances which are necessary for thermo-electric excitation, 
or which modify its action. In this respect the original expe¬ 
riment of Seebeck left much room for further investigation. 
When he had found that a brass wire coiled round the ends of 
a bar of antimony exhibited magnetic action by the application 
of heat to one of the extremities of the bar, it was still doubtful 
whether this effect might not depend either on some peculiarity 
in one or the other of these metals, on their contact, or on the 
mode of their juncture. 
The remarkable effects produced by helices in the hydro¬ 
electric circuit made it not improbable that much might depend 
on the wire being coiled round the bar. This was soon shown 
not to be the case, and that a circuit, however formed, provided it 
were composed of perfect conductors, was all that was necessary. 
Reasoning, again, from the analogy of the galvanic circuit, it 
might have been imagined that as three elements were neces¬ 
sary in the one, so two metallic elements with heat acting the part 
of the third might be required in the other; but it appeared from 
some of the earliest experiments, that metallic bars heated in con¬ 
tact with wires of the same metal gave considerable deviations 
with the galvanometer needle, and therefore that one metal alone 
sufficed for the development of thermo-electricity. The experi¬ 
ments of Dr. Trail in 1824 may be referred to this class; since, 
though made with slips of copper attached to the bar of antimony, 
yet, as the circuit was not completed through the copper, they 
properly exhibit the thermo-electricity of a single metal. One 
result, which is too important to be overlooked, is that the 
application of ice or heat to the centre of the bar produced 
opposite deviations in two needles placed between the centre 
and the extremities; whence he infers that “the direction of the 
compass needle may be considered as the resultant of two 
forces, the magnetism of composition of the earth, and its 
thermo-magnetism, which tends to place the needle east and 
west.” How far this coincides with subsequent experiments I 
shall have occasion to point out to you hereafter. 
But the most important researches on the thermo-electricity of 
a single metal were those made by Yelin in the same year; from 
which we learn, that all metallic bodies acquire magnetic pro¬ 
perties when unequally heated, and that the series of their mag¬ 
netic intensities when thus excited, is bismuth, antimony, zinc, 
silver, platina, copper, brass, gold, tin, lead :—that a metal acts 
differently according as the hot or cold part of it is placed 
