ic potential when in contact with any metal following
it in the series. He constructed a pile of metal disks consisting of
zinc and copper alternated and separated by wet cloths. At first he
believed that mere contact was sufficient, but when, later, it was shown
that chemical action took place, rapid progress was made in the
construction of voltaic cells. The next step after his pile was
constructed was to place pairs of strips of copper and zinc in cups
containing water or dilute acid. Volta received many honors for his
discovery, which contributed so much to the development of electrical
science and art--among them a call to Paris by Bonaparte to exhibit his
electrical experiments, and to receive a medal struck in his honor.

While Volta was being showered with honors, various scientific men with
great enthusiasm were entering new fields of research, among which was
the heating value of electric current and particularly of electric
sparks made by breaking a circuit. Late in 1800 Sir Humphrey Davy was
the first to use charcoal for the sparking points. In a lecture before
the Royal Society in the following year he described and demonstrated
that the "spark" passing between two pieces of charcoal was larger and
more brilliant than between brass spheres. Apparently, he was producing
a feeble arc, rather than a pure spark. In the years which immediately
followed many scientific men in England, France, and Germany were
publishing the results of their studies of electrical phenomena
bordering upon the arc.

By subscription among the members of the Royal Society, a voltaic
battery of two thousand cells was obtained and in 1808 Davy exhibited
the electric arc on a large scale. It is difficult to judge from the
reports of these early investigations who was the first to recognize the
difference between the spark and the arc. Certainly the descriptions
indicate that the simple spark was not being experimented with, but the
source of electric current available at that time was of such high
resistance that only feeble arcs could have been produced. In 1809 Davy
demonstrated publicly an arc obtained by a current from a Volta pile of
one thousand plates. This he described as "a most brilliant flame, of
from half an inch to one and a quarter inches in length."

In the library of the Royal Society, Davy's notes made during the years
of 1805 and 1812 are available in two large volumes. These were arranged
and paged by Faraday, who wa