I should premise,
that the system of telegraphing used upon the wires, during the
observation of February, 1852, was Bain's chemical. No batteries were
kept constantly upon the line, as in the Morse and other magnetic
systems. The main wire was connected directly with the chemically
prepared paper on the disc, so that any atmospheric currents were
recorded upon the disc with the greatest accuracy. Our usual battery
current, decomposing the salts in the paper, and uniting with the iron
point of the pen wire, left a light blue mark on the white paper, or,
if the current were strong, a dark one,--the color of the mark
depending upon the quantity of the current upon the wire.
"_Thursday, February 19, 1852_.
"Towards evening a heavy blue line appeared upon the paper, which
gradually increased in size for the space of half a minute, when a
flame of fire succeeded to the blue line, of sufficient intensity to
burn through a dozen thicknesses of the moistened paper. The current
then subsided as gradually as it, had come on, until it entirely
ceased, and was then succeeded by a negative current (which bleaches,
instead of coloring, the paper).
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