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.
He passed an electric current through a circuit, which was located close to another circuit containing a galvanometer, a device for showing the presence of an electric current and measuring its strength, but failed to obtain any result. He looked for such results only when the current had been fully established in the active circuit.
In one of his first successful experiments he wraps a coil of insulated wire around the soft iron bar that forms the armature or keeper of a permanent magnet of the horse-shoe type, and connects the ends of this coil to a galvanometer.
For some time after the cable was laid he remained at Valentia, endeavouring to bring his galvanometer to still greater perfection.
When so arranged a moistened piece of paper held several feet away will cause a minute expansion of the gelatine strip, which effects a pressure on the carbon, and causes a variation in the circuit sufficient to throw the spot of light from the galvanometer mirror off the scale.
He took my place, and in a moment the needle in the galvanometer responded to his grasp on the cylinder, exactly as the inventive philosopher had stated to be the due result of the experiment. I was startled. "But how came you, Mr. Margrave, to be so well acquainted with a scientific process little known, and but recently discovered?" "I well acquainted! not so.
The one marked B is so connected to the galvanometer and a reverser as to show the deflection caused by the induced currents, which are momentary in duration, and in the galvanometer circuit all on the same side of zero, for as the battery current on making contact produces an induced current in the reverse direction to itself, but in the same direction on breaking the contact, of course the one would neutralize the other, and the galvanometer would not be affected; the galvanometer connections are therefore reversed with each reversal of the battery current, and by that means the induced currents are, as you perceive, all in the same direction and produce a steady deflection.
Retarded clocks are sometimes employed as electric meters for registering the consumption of electricity. In these the current to be measured flows through a coil beneath the bob of the pendulum, which is a magnet, and thus affects the rate. In other meters the current passes through a species of galvanometer called an ampere meter, and controls a clockwork counter.
Currents sent from the opposite side were recorded by the galvanometer and the possibility of communication through the water was established. Others carried these experiments further, it being even suggested that messages might be sent across the Atlantic by this method.
Damon climbed into the rear seats of the odd-looking electric car, while Tom took his place at the steering wheel. "Are you all ready?" he asked. "Let her go!" fired back Mr. Sharp. "Bless my galvanometer, don't go too fast on the start," cautioned Mr. Damon, nervously. "I'll not," agreed the young inventor. "I want to get it warmed up before I try any speeding." He turned on the current.