Organ (Gr. organon, 'an instrument'), a musical instrument played by keys, and generally also by pedals, and consisting of metal and wood pipes, which sound by wind stored in bellows, and admitted into them at will. The following description is necessarily restricted to the most fundamental arrangements of this very complicated instrument. As met with in cathedrals and large churches, the organ comprises four or sometimes five departments, each in most respects a separate instrument with its own mechanism, called respectively the great-organ, the choir-organ, the swell-organ, the pedal-organ, and sometimes the solo-organ. Each has its own keyboard, but the different keyboards are brought into juxtaposition, so as to be under the control of one performer. Keyboards played by the hands are called manuals; by the feet, pedals. Three manuals, belonging to the choir, great, and swell organs respectively, rise above each other like steps in front of the performer, while the pedals by which the pedal-organ is played are placed on a level with his feet. The condensed air supplied by the bellows is conveyed through a wind-trunk into a wind-chest. Each department of the organ, it may be mentioned, has its wind-chest. Attached to the upper part of the wind-chest is the upper board, an ingenious contrivance for conveying the wind at pleasure to any individual pipe, or pipes, exclusively of the rest. In the upper board are set the pipes, of which a number of different quality, ranged behind each other, belong to each note. Beneath the upper board is a row of parallel grooves, running horizontally backwards, corresponding each to one of the keys of the instrument. On any of the keys being pressed down, a valve is opened which supplies wind to the groove belonging to it. The various pipes of each key stand in a line directly above its groove, and the upper surface of the groove is perforated with holes bored upwards to them. Were this the whole mechanism of the sound-board the wind on entering any groove would penetrate all the pipes of that groove; there is, however, in the upper board another series of horizontal grooves at right angles to those beneath, supplied with cross-slides, which can be drawn out or pushed in at pleasure by a mechanism worked by the draw-stops placed within the player's reach. Each slide is perforated with holes, which, when it is drawn out, complete the communication between the wind-chest and the pipes: the communication with the pipes immediately above any slide being, on the other hand, closed up when the slide is pushed in. The pipes above each slide form a continuous set of one particular quality, and each set of pipes is called a stop. Each department of the organ is supplied with a number of stops, producing sounds of different quality. The great-organ, some of whose pipes appear as show-pipes in front of the instrument, contains the main body and force of the organ. Behind it stands the choir-organ, whose tones are less powerful, and more fitted to accompany the voice. Above the choir-organ is the swell-organ, whose pipes are enclosed in a wooden box with a front of louvre-boards like Venetian blinds, which may be made to open and shut by a pedal, with a view of producing crescendo and diminuendo effects. The pedal-organ is sometimes placed in an entire state behind the choir-organ, and sometimes divided and a part arranged on each side. The most usual compass of the manuals is from C on the second line below the bass staff to F above the third ledger line over the treble staff; and the compass of the pedals is from the same C to the F between the bass and treble staves—i.e. two octaves and a half. The real compass of notes is, as will be seen, much greater.
Organ-pipes vary much in form and material, but belong to two great classes, known as flue-pipes and reed-pipes. A section of one of the former is represented in the figure. Its essential parts are the foot a, the body b, and a flat plate c, called the languge, extending nearly across the pipe at the point of junction of foot and body. There is an opening, de, in the pipe, at the spot where the languge is discontinuous. The wind admitted into the foot rushes through the narrow slit at d, and, in impinging against c, imparts a vibratory motion to the column of air in the pipe, the result of which is a musical note, dependent for its pitch on the length of that column of air, and consequently on the length of the body of the pipe: by doubling the length of the pipe we obtain a note of half the pitch, or lower by an octave. Such is the general principle of all flue-pipes, whether of wood or of metal, subject to considerable diversities of detail. Metal pipes have generally a cylindrical section, wooden pipes a square or oblong section. A flue-pipe may be stopped at the upper end by a plug called a tompion, the effect of which is to lower the pitch an octave, the vibrating column of air being doubled in length, as it has to traverse the pipe twice before making its exit. Pipes are sometimes half-stopped, having a kind of chimney at the top. The reed-pipe consists of a reed placed inside a metallic pipe. This reed is a tube of metal, with the front part cut away, and a tongue or spring put in its place. The lower end of the tongue is free, the upper end attached to the top of the reed; by the admission of air into the pipe the tongue is made to vibrate, and, in striking either the edge of the reed or the air, produces a musical note, dependent for its pitch on the length of the tongue, its quality being determined to a great extent by the length and form of the pipe or bell within which the reed is placed. When the vibrating tongue does not strike the edge of the reed, but the air, we have what is called the free reed, similar to what is in use in the Harmonium (q.v.). To describe the pitch of an organ-pipe terms are used derived from the standard length of an open flue-pipe of that pitch. The largest pipe in use is the 32-feet C, which is an octave below the lowest C of the modern pianoforte. There is, however, now in the new Sydney organ a pedal stop 64-feet tone. By a 32-feet or 16-feet stop we mean one whose lowest note is produced by a pipe 32 feet or 16 feet in length.
The stops of an organ do not always produce the note properly belonging to the key struck; sometimes they give a note an octave, or, in the pedal-organ, even two octaves lower, and sometimes one of the harmonics higher in pitch. Compound or mixture stops have several pipes to each key, corresponding to the different harmonics of the ground-tone. There is an endless variety in the number and kinds of stops in different organs; some are, and some are not continued through the whole range of manual or pedal. Some of the more important stops are called open or stopped diapason (a term which implies that they extend throughout the whole compass of the keyboard). The stops on an organ are principally of 8 feet in the manuals. The dulciana is an 8-feet manual stop, of small diameter, so called from the sweetness of its tone.
Among the reed-stops are the clarion, oboe, bassoon, vox humana, trumpet or posaune, and trombone or ophicleide, deriving their names from real or fancied resemblances to these instruments and to the human voice. Of the compound-stops the most prevalent in Britain is the sesquialtera—more frequently called mixture—consisting of three to five ranks of open metal pipes, often a 17th, 19th, 22d, 26th, and 29th from the ground-tone. The resources of the organ are further increased by appliances called couplers, by which a second manual and its stops can be brought into play, or the same manual can be united to itself in the octave below or above.
Organs are now generally tuned on the equal temperament (see TEMPERAMENT). The notation for the organ is in three staves, consisting of a treble and two bass clefs; but in old compositions the soprano, tenor, and alto clefs are used.
The organs used in antiquity were principally water-organs. Large water-organs were employed to accompany the performances at the Roman theatres, and similar instruments were to be found in the hippodromes of Constantinople. The scope of the instrument was therefore originally secular, and one of the earliest patrons of the organ was the Emperor Nero. Ctesibius of Alexandria must be credited with the invention of the organ. Taking the idea from a peculiar sort of clepsydra or water-clock which he had invented, and one function of which was to tell the hours of the night by musical notes, he worked onwards from invention to invention until he constructed the earliest water-organs. The instruments shown to Nero and the first organs ever seen in Rome were from the designs of Ctesibius. The water mechanism in the 'water-organs' was connected solely with the blowing, and seems to have been insisted on so strongly by the early organ-builders in order to render that operation equable and steady. By means of pistons working in cylinders the wind was pumped through water into the wind-chest, where were set the pipes, furnished on the bottom with slides, which were connected with iron keys by strings or trackers. Such was the main difference between the water-organ and the wind-organ. The water-organ became the rage of Rome and increased in favour as the empire hastened to its decline. In the reign of Honorius (400 A.D.) no nobleman's house was considered complete without its organ, and portable water-organs were made in great numbers which could be carried by slaves from house to house, where concerts or musical gatherings were attended by their masters. After the overthrow of the western empire organ-building seems to have been lost, among other useful arts, under the influence of the barbarian invasions. Constantinople, however, remained what it had always been, the great home of organ-building in the ancient world. The magnificence of the organs in the Golden Hippodrome is spoken of with enthusiasm by the Byzantine historians. An organ which was brought by certain Byzantine ambassadors on a mission to Charlemagne is said to have served as a model for the first organ ever built in mediæval Europe, constructed by the orders of that emperor according to the Greek pattern. From Aix-la-Chapelle the use of organs spread throughout Charlemagne's empire, and this instrument served as a model for the rest.
The application of bellows to the organ was known in the days of the later Roman emperors. On the obelisk of Theodosius we have a delineation of an organ blown solely by bellows. Probably the invention of the bellows mechanism dates from the time of the Emperor Julian. Yet this great secret of organ-building was rarely if ever acted upon; and until the end of the 9th century, when Germany had become the centre of organ-building, water-organs were the almost exclusive form of organ employed both in Europe and the East. Towards the end of the 9th century large bellows organs began to be built, in keeping with the large Romanesque churches of the times. Thirty bellows were employed in some of these organs; the outstretched arms of the organist could not span the compass of an octave; and the player or players struck each key with their fist. In the monasteries meanwhile, where size was not so much in demand, the mechanism of the organ was marvellously elaborated. The complete furnishings of the organ parts were manufactured in the monasteries, even down to the smelting of the metals whereof the pipes were made. Those diminutive organs, called regals, so small that they could be held on the palm of the hand, were the outcome of monastic ingenuity, and Pope Sylvester II. was a warm patron of organ-building, and himself no mean inventor in the art.
The family of the Antignati, in Brescia, had a great name as organ-builders in the 15th and 16th centuries. The organs of England were once in high repute, but the puritanism of the Civil War doomed most of them to destruction; and when they had to be replaced after the Restoration it was found that there was no longer a sufficiency of builders in the country. Foreign organ-builders were therefore invited to settle in England, the most remarkable of whom were Bernhard Schmidt (generally called Father Smith), his nephews, and Renatus Harris. Christopher Schreider, Snetzler, and Byfield succeeded them; and, at a later period, Green and Avery, some of whose organs have never been surpassed in tone. The largest English organs are those of the Royal Albert Hall, St Paul's Cathedral, the Alexandra Palace, the Crystal Palace, St George's Hall, Liverpool, and the Leeds Town-hall. The German organs are remarkable for preserving the balance of power well among the various masses, but in mechanical contrivance they are surpassed by those of England.
The largest organ in the world is usually said to be that in the cathedral of Seville, which is stated to have 110 stops and 5300 pipes. There are several organs in that cathedral, and this immense organ is said to exceed them all considerably in size. The method of blowing it is peculiar: a man walks up and down a long planking, arranged like the familiar 'see-saw,' the motion of which fills the bellows. Since, however, there is a conflict of testimony as to the Seville organ, and no certain indication of its magnitude can be gathered except by reports upon hearsay, the superiority in point of size among the organs of Europe is usually conceded to the Dutch organs. The organ in the cathedral of St Lawrence at Rotterdam is an immense structure, containing a great organ with 18 stops, a choir with 15, a positive with 18, an echo with 8, and a pedal-organ with 16 stops. These, along with 11 accessory stops, make up a total of 86 stops. The organ at the cathedral of St Bavon at Haarlem was long celebrated as the largest in the world. It took three and a half years to build, and cost £10,000. It possesses 4088 pipes and 60 stops, exclusive of accessory stops. The organ of the Protestant Church in Utrecht has 59 stops, including the accessory ones; that in the Octagon Church at Rotterdam possesses a total complement of 52 stops. St Peter's at Rome has four smallish organs, the largest of which has only 2 manuals and pedal, and 27 stops in all, thus divided—great, 17; swell, 6; pedal, 4. The second largest organ in St Peter's has but 1 manual and pedal. Generally speaking, the Italian organs are much inferior in point of size to those of the northern nations.
Up till the middle of the nineteenth century, little interest was taken in organ-building in America. The erection of the great organ in the Music Hall, Boston, by a German builder, Walcker of Wirtemberg, gave the first impetus to public interest in the matter. Roosevelt of New York, and Jardine, likewise of New York, are two of the best-known organ-builders in America at the present time. Roosevelt has invented 'the automatic adjustable combination,' which enables the player to place any required combination of stops under immediate control, and to alter such combinations as frequently as desired. By his construction of the wind-chest, also, each pipe has its own valve, actuated by compressed air. Among the largest organs in America are the organs of the Roman Catholic Cathedral, Montreal, the cathedral of the Holy Cross, Boston, which possesses 83 stops; the Music Hall, Cincinnati, with 96 stops and 4 manuals, and the Tremart Temple, Boston, with 65 stops.
For the structure of the organ, see Hopkins and Rimbault, The Organ (Lond. 1855). For the history of the organ, see Rowbotham's History of Music, vol. iii. chaps. 3, 6; and book iv. chap. 2 (Lond. 1887). For organ-playing, see Archer's Practical Organ Tutor, Best's School for the Organ, Stainer's The Organ. There are also works on the organ by Warman (1882-87) and Elliston (1894), and a very full organ bibliography in Notes and Queries for 1890. The American organ is discussed at HARMONIUM; and BARREL-ORGAN is a separate article.