pipe seen in front leads to the burner, and the wires WW connected
to the extreme bars or poles are the electrodes of the pile.

Thermo-piles are interesting from a scientific point of view as a
direct means of transforming heat into electricity. A sensitive
pile is also a delicate detector of heat by virtue of the current
set up, which can be measured with a galvanometer or current
meter. Piles of antimony and bismuth are made which can indicate
the heat of a lighted match at a distance of several yards, and
even the radiation from certain of the stars.

Thermo-batteries have been used in France for working telegraphs,
and they are capable of supplying small installations of the
electric light or electric motors for domestic purposes.

The action of the thermo-pile, like that of a voltaic cell, can be
reversed. By sending a current through the couple from the
antimony to the bismuth we shall find the junction cooled. This
"Peltier effect," as it is termed, after its discoverer, has been
known to freeze water, but no practical application has been made
of it.

A very feeble thermo-electric effect can be produced by heating
the junction of two different pieces of the same substance, or
even by making one part of the same conductor hotter than another.
Thus a sensitive galvanometer will show a weak current if a copper
wire connected in circuit with it be warmed at one point.
Moreover, it has been found by Lord Kelvin that if an iron wire is
heated at any point, and an electric current be passed through it,
the hot point will shift along the wire in a direction contrary to