KEYS of an Organ, Harpsichord, &c. those little pieces in the fore part of those instruments, by means whereof the jacks play so as to strike the strings. These are in number 28 or 29. In large organs there are several sets of the keys, some to play the secondary organ, some for the main body, some for the trumpet, and some for the echoing trumpet, &c.: in some there are but a part that play, and the rest are only for ornament. There are 20 slits in the large keys which make half notes. See the article ORGAN, &c.