Sodium
Lead
Tin
Copper
Platinum
Silver
Zinc
Cadmium
Arsenic
Iron
Red phosphorus
Antimony
Tellurium
Selenium
NEGATIVE

Other things being equal, the hotter the joint in comparison with
the free ends of the bars the stronger the current of electricity.
Within certain limits the current is, in fact, proportional to
this difference of temperature. It always flows in the same
direction if the joint is not overheated, or, in other words,
raised above a certain temperature.

The electromotive force and current of a thermo-electric couple is
very much smaller than that given by an ordinary voltaic cell. We
can, however, multiply the effect by connecting a number of pairs
together, and so forming a pile or battery. Thus figure 23 shows
three couples joined "in series," the positive pole of one being
connected to the negative pole of the next. Now, if all the
junctions on the left are hot and those on the right are cool, we