al utility of
such a light for illuminating purposes was still a thing of the future.
The expense of constructing and maintaining such an elaborate battery,
and the rapid internal destruction of its plates, together with the
constant polarization, rendered its use in practical illumination out of
the question. It was not until another method of generating electricity
was discovered that Davy's demonstration could be turned to practical
account.

In Davy's own account of his experiment he says:

"When pieces of charcoal about an inch long and one-sixth of an inch in
diameter were brought near each other (within the thirtieth or fortieth
of an inch), a bright spark was produced, and more than half the volume
of the charcoal became ignited to whiteness; and, by withdrawing the
points from each other, a constant discharge took place through the
heated air, in a space equal to at least four inches, producing a most
brilliant ascending arch of light, broad and conical in form in the
middle. When any substance was introduced into this arch, it instantly
became ignited; platina melted as readily in it as wax in a common
candle; quartz, the sapphire, magnesia, lime, all entered into fusion;
fragments of diamond and points of charcoal and plumbago seemed to
evaporate in it, even when the connection was made in the receiver of an
air-pump; but there was no evidence of their having previously undergone
fusion. When the communication between the points positively and
negatively electrified was made in the air rarefied in the receiver of
the air-pump, the distance at which the discharge took place increased
as the exhaustion was made; and when the atmosphere in the vessel
supported only one-fourth of an inch of mercury in the barometrical
gauge, the sparks passed through a space of nearly half an inch; and, by
withdrawing the points from each other, the discharge was made through
six or seven inches, producing a most brilliant coruscation of purple
light; the charcoal became intensely ignited, and some platina wire
attached to it fused with brilliant scintillations and fell in large
globules upon the plate of the pump. All the phenomena of
chemical decomposition were produced with intense rapidity by this
combination."(1)

But this experiment demonstrated another thing besides the possibility
of producing electric light and chemical decomposition, this being the
heating power capable of being produced by the electric current. Thus