Collier's New Encyclopedia (1921)/Tuning Fork
TUNING FORK, an instrument of steel, consisting of two prongs, branching from a short handle, which, when set in vibration, gives a musical note. It was invented by John Shore, in 1711. Though the pitch of forks varies slightly with changes of temperature, or by rust, etc., they are the most accurate means of determining pitch. They are capable of being made of any pitch within certain limits, but those most commonly used are the notes A and C, giving the sounds represented by the second and third spaces in the treble stave. The vibration number of the note C varies from 518 (French diapason-normal) and 528 (Scheibler-medium) to 540 and 544 (Philharmonic).