The establishment of periodic movement in one body by impulses of the
same period communicated to it from another body in motion. Thus if two
tuning forks are of the same pitch and one is sounded the other will
begin to sound by sympathy, the sound waves communicating the necessary
periodic impulses to it.

Sympathetic vibrations are utilized in harmonic telegraphy. (See
Harmonic Receiver–Telegraph, Harmonic.)