Queenstown; but it was not of so serious a character as to offer any
substantial obstacle to the passage of the electric current.

As everything pertaining to the actual operation of the Atlantic Cable
has been studiously withheld from the public, until it has come to be
seriously doubted whether any despatches were ever transmitted through
it, we presume it will not be out of place here to give the actual
_modus operandi_ of this great wonder and mystery.

The only instrument which could be used successfully in signalling
through the Atlantic Cable was one of peculiar construction, by
Professor Thompson, called the marine galvanometer. In this instrument
momentum and inertia are almost wholly avoided by the use of a needle
weighing only one and a half grains, combined with a mirror reflecting a
ray of light, which indicates deflections with great accuracy. By these
means a gradually increasing or decreasing current is at each instant
indicated at its due strength. Thus, when this galvanometer is placed
as the receiving instrument at the end of a long submarine cable, the
movement of the spot of light, consequent on the completion of a circuit
through the battery, cable, and earth, can be so observed as to furnish
a curve representing very accurately the arrival of an electric current.
Lines representing successive signals at various speeds can also be
obtained, and, by means of a metronome, dots, dashes, successive _A_-s,
etc., can be sent with nearly perfect regularity by an ordinary Morse
key, and the corresponding changes in the current at the receiving end
of the cable accurately observed. The strength of the battery employed
was found to have no influence on the results; curves given by batteries
of different strengths could be made to coincide by simply drawing them
to scales proportionate to the strengths of the two currents. It was
also found that the same curve represented the gradual increase of