From this phenomenon, the chemical action of acids upon metals and the production of an electric current were observed, and the voltaic pile was invented. This consisted of alternate discs of copper and zinc, separated by layers of cloth steeped in an acidulated solution. This was the invention of Volta. From this grew the Daniell battery, invented in 1836 by Prof. Daniell of London, quickly followed by those of Grove, Smee, and others. These batteries were more constant or uniform in the production of electricity, were free from odors, and did not require frequent cleaning, as did the plates of the voltaic pile, which were important results for telegraphic purposes. The Daniell battery in its original form employed an acidulated solution of sulphate of copper in a copper cell containing a porous cup, and a cylinder of amalgamated zinc in the porous cup and surrounded by a weak acid solution. In the illustration, which shows a slightly modified form, a cruciform rod of zinc within a porous cup is surrounded by a copper cell, the whole being enclosed within a glass jar. [Illustration: FIG. 2.--DANIELL’S BATTERY.] The second element of the telegraph--the conducting wire--was scarcely an invention in itself, and the fact that electricity would act at a distance through a metal conductor had been observed many years before the Morse telegraph was invented. In 1823, however, Weber discovered that a copper wire which he had carried over the houses and church steeples of Göttingen from the observatory to the cabinet of Natural Philosophy, required no special insulation. This was an important observation in the practical construction of telegraph lines. One of even greater importance, however, was that of Prof. Steinheil, of Munich, who, in 1837, made the discovery of the practicability of using the earth as one-half, or the return section, of the electric conductor. [Illustration: FIG. 3.--PROF. HENRY’S INTENSITY MAGNET.]