174 REPORT—1862. 
The currents were clearly not due to chemical action on the wires; for, in 
the first place, currents of considerable strength were obtained from two per- 
fectly homogeneous platinum wires, flowing from hot to cold across the loose 
contact ; and in the second place, the direction of the current was different in 
copper and iron, whereas the chemical action undergone by the wire was alike 
in the two cases. 
The researches of Becquerel, Pouillet, Buff, Hankel, and Grove were ex- 
amined, to see whether the electricity produced during combustion, or the 
properties of flame, would account for the currents, but it was found that all 
the electrical effects produced by flame could be divided into two classes : first, 
phenomena depending on the relative position of the two wires in the flame ; 
and secondly, phenomena depending on the voltaic couple formed by the 
metals used, and the hot vapour acting as an electrolyte between them. My 
results were independent of the position of the wires in the flame, and could 
not be accounted for by supposing these wires to form a voltaic couple, inas- 
much as though in some cases, where wires of two metals were looped together 
as described, the current flowed from the metal most attacked across the 
imaginary electrolyte to the other wire, in other cases it flowed in the oppo- 
site direction. 
It remained to be seen whether the currents might not have a thermo- 
electric origin. Last year I imagined that the effect observed might be di- 
rectly due to discontinuity, but that idea was dispelled by some experiments 
with loose contacts between wires of different metals, which have thrown 
great light on the question. 
Loops of iron, silver, platinum, gold, and copper wires were combined two 
by two in all the possible arrangements, and the currents measured which 
were obtained when one or the other or both loops were heated with loose 
and tight contacts between them. 
A Table was thus formed, which is appended to the present paper. 
The resistance of the circuit was so large (2050 x 10°, Weber’s absolute 
aoe that the inherent resistance of the joint and of the different short 
wires used in each experiment could be neglected, and the deflections ob- 
tained on a reflecting galvanometer could be taken as approximatively pro- 
portional to the electromotive force of each combination. The common 
thermo-electric currents produced by the metallic contact between dissimilar 
wires almost vanish in comparison with those produced by the loose contacts. 
T need not present a complete analysis of the Table, but will speak only of 
the combination of iron and copper with which the most remarkable results 
were obtained. When the usual tight metallic contact was made between 
these two wires and the two loops equally heated, the current first flowed 
from copper to iron across the joint, and then as the temperature rose ceased 
altogether, and finally, at a red or white heat, flowed from iron to copper. 
The maximum deflection obtained in either direction was three divisions. 
These deflections showed the celebrated inversion discovered by Cumming. 
If the pressure between the loops was relaxed, the current ceased alto- 
gether ; but when the loops were moved, so that the copper became red-hot 
while the iron was cool, a current flowed from the copper to the iron, or from 
hot to cold across the joint, giving a deflection of 100 divisions; whereas if 
the iron was heated red-hot and the copper cooled, a current giving 90 divi- 
sions flowed in the opposite direction, or from iron to copper, but from hot 
to cold as before. Thus in these two cases the loose-contact currents given 
when one or the other loop was heated, flowed in the opposite direction be- 
