s destined to contribute greatly to the
future development of the science and art of electricity. In one of
these volumes is found an account of a lecture-experiment by Davy which
certainly is a description of the electric arc. An extract of this
account is as follows:

The spark [presumably the arc], the light of which was so
intense as to resemble that of the sun, ... produced a
discharge through heated air nearly three inches in length, and
of a dazzling splendor. Several bodies which had not been fused
before were fused by this flame.... Charcoal was made to
evaporate, and plumbago appeared to fuse in vacuo. Charcoal was
ignited to intense whiteness by it in oxymuriatic acid, and
volatilized by it, but without being decomposed.

From a consideration of his source of electricity, a voltaic pile of two
thousand plates, it is certain that this could not have been an electric
spark. Later in his notes Davy continued:

...the charcoal became ignited to whitness, and by withdrawing
the points from each other, a constant discharge took place
through the heated air, in a space at least equal to four
inches, producing a most brilliant ascending arch of light,
broad and conical in form in the middle.

This is surely a description of the electric arc. Apparently the
electrodes were in a horizontal position and the arc therefore was
horizontal. Owing to the rise of the heated air, the arc tended to rise
in the form of an arch. From this appearance the term "arc" evolved and
Davy himself in 1820 definitely named the electric flame, the "arc."
This name was continued in use even after the two carbons were arranged
in a vertical co-axial position and the arc no more "arched." An
interesting scientific event of 1820 was the discovery by Arago and by
Davy independently that the arc could be deflected by a magnet and that
it was similar to a wire carrying current in that there was a magnetic
field around it. This has been taken advantage of in certain modern
arc-lamps in which inclined carbons are used. In these arcs a magnet
keeps the arc in place, for without the magnet the arc would tend to
climb up the carbons and go out.

In 1838 Gassiot made the discovery that the temperature of the positive
electrode of an electric arc is much greater than that of the negative
electrode. This is explained in electronic theory by the bombardment of
the positive electrode by