of Electro-Magnetism by Heat. 59 
bismuth will be only 7°, and 9° for the last 560 of antimony ; or, 
in other words, the deviation in bismuth by 175°, reckoning from 
65° to 240°, is double that by 235°, from 240° to 475°; and, in anti- 
mony, the deviation by the first 175° exceeds that by the last 
560°. - 
The experiments which have hitherto been detailed, rest upon 
the supposition that the agency of heat in exciting the magnetic 
electricity is effective on the bars alone, and that the action of the 
wires is solely to conduct the electricity thus excited. This is not 
the fact. When the extremity of a bar is heated in connexion with 
a wire, the wire is itself in the same state with the bar, having 
its extremities at different temperatures: the total effect is therefore 
the sum or difference of that of the bar and wire, accordingly as 
their relations to heat and electricity are different or the same. 
If a bar of bismuth be connected with the galvanoscope by wires 
of antimony, it is obvious, from the experiment of the double bars, 
that its effect is increased by the conspiring action of the antimony ; 
had the wires been of platina, the effects would, for the same 
reason, have been diminished. This would be the case, not merely 
from platina being either a better or worse conductor of heat than 
bismuth or antimony, but because its electrical properties, as de- 
veloped by heat, are similar, though inferior to those of bismuth ; 
and therefore when heated in contact with bismuth, its action is 
in the opposite direction. As the metals differ materially, not only 
in the nature, but in the strength of their action, it may happen, 
when the energy of the bar is weak in comparison with that of the 
wire, that their joint action will be nearly the same as that of the 
wire alone. This was the case in the experiment with the bar of 
brass, heated with silver and platina wires*. For, though when 
brass and silver, or brass and platina wires of the same size are 
* This experiment would be yet more decisive with wires of gold and platina. 
H 2 
