A musical instrument approved and used by the Church to assist in public worship. The pipe organ, being the more popular, is used in most churches. Organs with two or more manuals or keyboards are mentioned as early as 1350. The swell with movable shutters, varying the sound volume, was invented around 1712. Modern church organs are supplied with air by electric blowers. The Roman Order permits its use on Gaudete and Laetare Sundays and on Maundy Thursday until the Gloria, and on Holy Saturday from the Gloria on. Though other instruments are allowed at church services, the organ's majestic tone makes it appropriate for divine service. In 1968 the Holy See authorized the use of musical instruments other than the organ in liturgical services, "provided they are played in a manner suitable to worship."