"The incident behind the invention of telephone"
The incident that ultimately led to the invention of the telephone occurred while Bell and his assistant, Thomas A. Watson, were trying out various methods for sending sound over wire. Up to that time, the sound moving over a wire varied only in length, like the dots and dashes of the telegraph.
The two scientists, in adjoining rooms, were tuning reeds on opposite ends of a wire. By chance, one of Watson's reeds became screwed down so tightly that it "froze" to the pole of the electromagnet. As he plucked it to free it, he sent an impulse over the wire with a distinctive sound, different from dots and dashes. Bell heard the sound with its tones and overtones.
Rushing into his aide's room, he shouted: "Watson, what did you do then? Don't change anything... "