The tuning of organs is a subject on which there is much difference of opinion. Some tune from c, on the unequal temperament, and throw the imperfections on what is called the wsv/f, or key of four flats. Others tune from A, and adopt the equal temperament ; this latter cer tainly has the better reasoning in its form, as it approaches nearer to the human voice, interferes less with the band, and is more agreeable in general modulation. This subject has been minutely handled by some scientific writers, who have given themselves the trouble of what may be called splitting octaves into smaller inh'rrals. But the advant ages of this minuteness have not yet extended beyond the schemers themselves, for not ono of their methods has yet left the cradle of its birth. The Temple organ is said to have 14 sounds in the octave ; the Foundling, 16; Ilawke's patent, 17 ; Loeschnum has 24, and Liston's enharmonic organ as many as 59, of which 24 are on the keys, and the rest on the pedals and other contrivances. If such schemes were to become general, they would make practical men tremble ; but flat fifths aro still in use notwithstanding the enharmonic divisions, and they have nothing to fear beyond an occasional dispute on the subject.
The numbers and kinds of stops are matters not subject to rule ; they vary in almost every organ, and seem more under the command of circumstances, such as space and price, than any other parts of the instrument In treating the mechanism of the organ in so general a manner, we shall hardly be expected to point out all the improvements which have been made of late years in its various parts : a few however may be mentioned. Considerable strength both of hand and foot, as well as consummate musical skill, are required in an organist; the expenditure of wind also may vary from a few hundred to many thousand cubic feet per second. With a small expenditure of wind there is a greater elasticity of the air, and consequently a greater pressure against the valves so as to make them more difficult to open. The remedy for this was 31r. Barker's Pneumatic Lover, in which the elasticity of the air itself is made to overcome the resistances which hail previously been thrown upon the organist. Mr. Willis has a contrivance for admitting wind to the pipes of the pedal-organ ; it is formed by covering the aperture with a piece of leather, fixed at one end, and attached at the other to a wooden roller, so that when the latter is moved by the pedal key, it wraps the leather round it and so uncovers the opening, when the key is released a spring brings the roller back, and by un rolling the leather, again covers the aperture. Mr. Bishop's Composition Pedals, for opening and shutting the stops by the foot instead of the hand, are of great value, as is also his Anti-concussion apparatus for preventing the pulsation or concussion of air in the wind-chest, when a large number of pipes are made to cease speaking suddenly and a few only aro held on. Mr. Willis has also introduced mechanical improvements for producing crescendo and diminuendo effects, enabling the player to draw or shut off any required numher of the stops, one after the other in succession by one continuous movement, in contra distinction to the intermittent or repetition movements. Mr. Holt has introduced the pneumatic lever, or valve, topped-pipes, so that when the wind is admitted it expands and causes a spring or jack tipped with india-rubber to strike the tongue and set it in motion, similar to the contrivance explained under iiAltMONI031. The wind then keeps up the vibrations. By this contrivance the reeds may bo made of thicker metal, and a fuller, rounder tone be produced. Lorenzi, of Paris, has introduced various novelties. The highly ex pressive tones of the organ depend principally on a repetition of sounds which succeed each other as the keys are touched. The keys act upon two stops, the first upon one pipe, and the second upon another in unison with it. The sound-board is divided into two parts with double
valves, so that those of the first part admit wind to the pipes which are acted on only by the first stop, and those of the other part admit wind to the pipes which are acted ou by the other stop. By pressing the key lightly to the first stop, and playing one not° only, a soft sweet sound is produced; and by depressing the key entirely, the second stop is brought into action, and greater expression and power are thus attained. In this arrangement there may be a single sound-board in two parts, or two separate sound-boards may be used. The notes of the' first part, particularly of the flute, bugle, and trombone stops, are of great deli cacy and sweetness; and those of the other part, produced by the second series of stops, are of the greatest power and are occasionally double. The transition from piano to forte is not perceptible when the second note is commenced, but it is necessary to separate the first from the second part of the sound-board, as also of the pipes by en closing them in a swell-box. By opening the swell the full power of the notes is obtained, without any violent transposition from piano to forte. The mechanism for effecting this is attached to a pedal, so that it may be disengaged from the keys when required. Another mode of giving expression and increasing the force by vibration or trembling, and increasing and decreasing the sound, when applied to the lone chromic organ with two valves, allows the performer gradually to augment the sound to double its usual force, and to diminish it again in the same manner, thus producing effects of a novel and delightful character. In order to obtain this result, an expansive bellows is em ployed; this forms a reservoir, and at the same time (on opening a valve) Increases the force of the air nearly twofold. It is divided longitudinally into two parts, the part answering to ordinary bellows occupying three-fifths, the other part two-fifths, so as to make two bellows united. This smaller part communicates with the larger by means of a small valve placed above the hole, by which this second part receives the supply of air. There is also a valve which should remain open, and beside it another valve applied to a hole for the pur pose of discharging the air from this part of the bellows. A very simple mechanism is employed for opening this latter discharging valve (no matter of what size the opening may be) and of shutting the other, so as to atop the communication with the other part of the bellows. By means of this mechanism, when the smaller bellows has discharged itself into the greater, the power of the latter is nearly doubled. It is worked by the same pedal which applies the trembling sound, and the same pedal also acts upon the swell-box the second series of pipes. These three movements are so arranged, that in depressing lightly the pedal, it acts only upon the mechanism of the trembling sound attached to the pipes acted upon by the first series of stops, and makes that note only vibrate ; by depressing the key to the second stop the power of the note is greatly increased, and by then depressing the pedal further the note still increases in power ; finally, when the pedal acts upon the mechanism of the expansive bellows, it gives a great volume of sound. The reverse process gradually dimi nishes the sound, but to reduce it to another pedal or lever under the key-board, worked with the knee (and hence called a gensal), shuts some of the jalousies or lower-boards of tho case enclosing the first series of pipes, and by this means the note is further diminished in force. These jalousies are disposed like those for the second series of pipes, but with the difference that in their state of repose they are open.