in general, is an instrument or machine designed for the production of some certain action or operation; in which sense, the mechanic powers, machines, and even the veins, arteries, nerves, muscles, and bones of the human body, may be called organs.

ORGAN, in music, the largest and most harmonious wind-instrument.

The invention of the organ is very ancient, though it is agreed that it was very little used till the eighth century. It seems to have been borrowed from the Greeks. Vitruvius describes an hydraulic one in his tenth book of architecture. The emperor Julian has an epigram in its praise. St. Jerome mentions one with twelve pair of bellows, which might be heard a thousand paces, or a mile; and another at Jerusalem, which might be heard at the mount of Olives.

There is one in the cathedral church of Ulm, in Germany, that is ninety-three feet high, and twenty-eight broad; the biggest pipe is thirteen inches in diameter; and it has sixteen pair of bellows.

The modern organ is a buffet, containing several rows of pipes. The size of the organ is generally expressed by the length of its biggest pipe; thus we say an organ of thirty-two feet, of sixteen, of eight, and of two feet.

Hydraulic Organ, denotes a musical machine that plays by means of water instead of wind. Of these there are several in Italy in the grottoes of vineyards. Ctesibius of Alexandria, who lived in the time of Ptolemy Euergetes, is said to have first invented organs that played by compressing the air with water, as is still practised. Archimedes and Vitruvius have left us descriptions of the hydraulic organ.