O'Reilly V. Morse - Background

Background

The problem that would-be telegraphers faced in the early 19th century is explained in the Court's opinion:"The great difficulty in their way was the fact that the galvanic current, however strong in the beginning, became gradually weaker as it advanced on the wire; and was not strong enough to produce a mechanical effect, after a certain distance had been traversed.” To send a signal from Baltimore to Washington would require thousands of volts and high currents – not feasible at a time when managing to make a pickled frog’s legs twitch, as Luigi Galvani and Alessandro Volta did, was the major achievement of the electro-galvanic force.

Samuel Morse’s “plan combining two or more electric or galvanic circuits, with independent batteries for the purpose of overcoming the diminished force of electromagnetism in long circuits.” The concept is illustrated in the figure shown at the right. Morse inserted the relays (or “repeaters” as the opinion terms them) at intervals sufficiently short (say, every 15 to 20 miles) that the signal was restored regularly to substantially its initial level before the noise could swamp it out.

The effect of Morse's use of "repeaters" is shown in the figure at the left, a graph of signal amplitude (with noise) vs. distance. The signal decays between repeaters, but Morse restores the signal to a predetermined level before it falls into the noise. That permits the message to be sent to great distances, which was previously not feasible.