ent, but simply, by means of it, to show what varying shapes a
given amount of energy can assume while maintaining unvarying
quantitative stability. When that form of power which we call an
electric current passes through Grove's battery, zinc is consumed in
acidulated water; and in the battery we are able so to arrange matters
that when no current passes no zinc shall be consumed. Now the
current, whatever it may be, possesses the power of generating heat
outside the battery. We can fuse with it iridium, the most refractory
of metals, or we can produce with it the dazzling electric light, and
that at any terrestrial distance from the battery itself.

We will now, however, content ourselves with causing the current to
raise a given length of platinum wire, first to a blood-heat, then to
redness, and finally to a white heat. The heat under these
circumstances generated in the battery by the combustion of a fixed
quantity of zinc is no longer constant, but it varies inversely as the
heat generated outside. If the outside heat be nil, the inside heat
is a maximum; if the external wire be raised to a blood-heat, the
internal heat falls slightly short of the maximum. If the wire be
rendered red-hot, the quantity of missing heat within the battery is
greater, and if the external wire be rendered white-hot, the defect is
greater still. Add together the internal and external heat produced
by the combustion of a given weight of zinc, and you have an
absolutely constant total. The heat generated without is so much lost
within, the heat generated within is so much lost without, the polar
changes already adverted to coming here conspicuously into play. Thus
in a variety of ways we can distribute the items of a never-varying
sum, but even the subtle agency of the electric current places no
creative power in our hands.

Instead of generating external heat, we may cause the current to
effect chemical decomposition at a distance from the battery. Let it,
for example, decompose water into oxygen and hydrogen. The heat
generated in the battery under these circumstances by the combustion
of a given weight of zinc falls short of what is produced when there
is no decomposition. How far short? The question admits of a
perfectly exact answer. When the oxygen and hydrogen recombine, the
heat absorbed in the decomposition is accurately restored, and it is
exactly equal in amount to that missing in the battery. We may, if we
lik