In this diagram, 1 and 2 are tuned reeds; 1A 2A are receivers tuned to the reeds 1 and 2 respectively; 1 and 1A are in unison, also 2 and 2A, but the two groups (the 1s and the 2s) differ from each other in pitch.
There were two ways of reading by the harmonic method. One was by the long and short tone-sounds and the other by the ordinary sounder.
The vibration of the receiving-reed was made to open and close a local circuit like a common Morse relay and thus operate the sounder. It is useless to try to send a message if the sender and receiver are out of tune with each other in this system.
What is true in science is true in life. If we are out of tune with our surroundings we only beat the air, and our efforts are in vain. We get no sympathetic response.