e, bottle up the gases, carry in this form the heat of the battery
to the polar regions, and liberate it there. The battery, in fact is
a hearth on which fuel is consumed; but the heat of the combustion,
instead of being confined in the usual manner to the hearth itself,
may be first liberated at the other side of the world.

And here we are able to solve an enigma which long perplexed
scientific men, and which could not be solved until the bearing of the
mechanical theory of heat upon the phenomena of the Voltaic battery
was understood. The puzzle was, that a single cell could not
decompose water. The reason is now plain enough. The solution of an
equivalent of zinc in a single cell develops not much more than half
the amount of heat required to decompose an equivalent of water, and
the single cell cannot cede an amount of force which it does not
possess. But by forming a battery of two cells instead of one, we
develop an amount of heat slightly in excess of that needed for the
decomposition of the water. The two-celled battery is therefore rich
enough to pay for that decomposition, and to maintain the excess
referred to within its own cells.

Similar reflections apply to the thermo-electric pile, an instrument
usually composed of small bars of bismuth and antimony soldered
alternately together. The electric current is here evoked by warming
the soldered junctions of one face of the pile. Like the Voltaic
current, the thermo-electric current can heat wires, produce
decomposition, magnetise iron, and deflect a magnetic needle at any
distance from its origin. You will be disposed, and rightly disposed,
to refer those distant manifestations of power to the heat
communicated to the face of the pile, but the case is worthy of closer
examination. In 1826 Thomas Seebeck discovered thermo-electricity,
and six years subsequently Peltier made an observation which comes
with singular felicity to our aid in determining the material used up
in the formation of the thermo-electric current. He found that when a
weak extraneous current was sent from antimony to bismuth the junction
of the two metals was always heated, but that when the direction was
from bismuth to antimony the junction was chilled. Now the current in
the thermo-pile itself is always from bismuth to antimony, across the
heated junction--a direction in which it cannot possibly establish
itself without consuming the heat imparted to the junction. This heat