The young professor had been toiling over it for three years and it had constantly baffled him, until, on this hot afternoon in June, 1875, he heard an almost inaudible sound--a faint TWANG--come from the machine itself.
For an instant he was stunned.

He had been expecting just such a sound for several months, but it came so suddenly as to give him the sensation of surprise.

His eyes blazed with delight, and he sprang in a passion of eagerness to an adjoining room in which stood a young mechanic who was assisting him.
"Snap that reed again, Watson," cried the apparently irrational young professor.

There was one of the odd-looking machines in each room, so it appears, and the two were connected by an electric wire.

Watson had snapped the reed on one of the machines and the professor had heard from the other machine exactly the same sound.