(Greek: organon, an instrument)
A musical instrument used and approved by the Church as an aid to public worship.
Because of its sonorous and majestic tone it is most appropriate for use in religious services.
Organs are of two varieties, the pipe organ and the reed organ.
The former, being the more powerful, is generally used in churches.
It consists of tubes of wood and metal called organ-pipes, with a bellows and wind-chest, and is equipped with "stops," by which the tones of various instruments are imitated.
There is no authority for the story that the organ was invented or used by Saint Cecilia, the patroness of music, with whom it is associated as an emblem of art.
It was evolved gradually from the simple "Pan's pipes," or syrinx, a set of tubes bound together by attaching a bellows and a sliding perforated plate which opened and closed the tubes, said to have been invented by a certain Caesibius.
Organs of large size, with two or more "manuals," or keyboards, are mentioned as early as 1350.
The "coupler," an ingenious device for playing two or more notes of different octaves with one key, came into use c.1450, and stops were added c.1500.
The "swell" (movable shutters varying the volume of sound), was invented by Jordan, an Englishman, in 1712.
Reed organs, having vibrating metal tongues instead of pipes, came into use c.1500.
Modern church organs are supplied with air by powerful electric blowers.
Other musical instruments are allowed in church under certain restrictions, with the sanction of the bishop.
New Catholic Dictionary