274 Upon Caloric as a Cause of Galvanic Currents. 
by heat. The currents produced by fragments of ‘gold, are always 
feeble, and when copper is also present, the oxidation at the opie 
makes it almost impossible to distinguish any effect. 
‘Tin and lead furnish very equivocal results, even when one por- 
tion of the metal is as cold as ice, and the other heated, nearly to 
fusion. This is perhaps owing, in a great degree, to oxidation. 
Zine and silver must be heated in a coal fire and large bars used in 
order to obtain currents of sufficient force. The arsenic, employed, 
was the crude article of the shops; but its indications were sufficient- 
ly conspicuous when one of the fragments was heated until - white 
vapor of arsenious acid appeared. 
When dissimilar metals form the thermo-electric circuit, we do 
not perceive the relation which the elements have towards caloric. 
Becquerel is of opinion that the forces, as observed by him, bear a 
direct relation to the radiating power of the combined metals, (Ann. 
de Chimie &c. 1829,) but, most assuredly, this explanation is not ap~ 
plicable to the combination of portions of the same metal, and it ap- 
pears obvious, that in such cases, the direction and intensity of the 
current result from the course which the caloric takes, bron 3 its 
transmission from the hot portion to the cold. 
It appears evident from the results furnished in the foregoing table, 
that the metals naturally divide themselves into two classes; in the 
one (including bismuth, nickel, mercury, iron, gold, zine, tin and 
lead) the positwe galvanic current moves in opposition to the caloric; 
in the other, (consisting of silver; copper, platinum, arsenic and an- 
timony,) these currents coincide. The cause of this difference is by 
no means apparent, but it is obvious that it must operate with equal 
force in modifying the currents produced by the contacts of different 
metals. Pursuing the principles of investigation already described, 
for elementary combinations, it is easy to determine the influence 
which caloric exerts upon compound thermo-electric circuits, or 
those consisting of dissimilar substances. The process consists in 
connecting each metal with the galvanic multiplier; one of them is 
then to be heated, in order to ensure the direction of the caloric, 
and in this state, made to touch the other metal which — its 
natural temperature. 
he result invariably proved to be that the caloric, procouing’ in 
one direction, which varies, however, for each combination, . either 
diminishes, destroys or inverts the currents which the same metals 
