Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/900

834 ORGAN Second pedal. Arrange nient of manuals Composi tions. General mechan ism. by 8 -foot tone. For the purpose of realizing this as a general direction the soft 16-foot and 8-foot stops are re quired ; large instruments are, however, occasionally found which possess nothing of the kind. The following stops of higher pitch are occasionally found on the pedal : 5J twelfth bass, 4 fifteenth bass, mixture, and 4 clarion. These serve to make the pedal tone practically independent of coupling to the manual, which is a matter of great importance, especially in the per formance of certain compositions of Bach and other writers, who appear to have been independent of couplers. The 8-foot and 4-foot reeds on the pedal afford the best, indeed almost the only means of performing some types of composition best known in the works of Bach, in which the pedal sounds a chorale in the 8-foot or 4-foot pitch, whilst an elaborate accompaniment is executed on the manuals. Where these pedal reeds are not present it is necessary to couple to the pedal an 8 -foot or a 4 -foot manual reed. The corresponding manual ceases to be available for the manual part of the composition ; and, as this generally involves two manuals, one of which must possess a 16-foot stop, the performance is sometimes im practicable, even on large organs. In some foreign instruments two sets of pedals are pro vided, which may be described as great and choir pedals. The great pedal is in the usual position ; the choir pedal is in front of the other, and sloping. It is so placed that the feet rest on it naturally when stretched out in front of the performer. There is a choir pedal of this kind in the organ in the minster at Ulm, built by Walcker of Ludwigsburg. It is a very large instrument, having 100 sounding stops. It has no compositions, which indeed are but little known in Germany; and without some arrangement such as this a soft pedal would hardly be obtainable. There are a few other instruments which have choir pedals, but they have not been introduced into England. In organs which have a single manual the characteristics of the great and choir organs are usually united. In organs which have two manuals the lower usually repre sents the united great and choir, the upper is the swell. In organs which have three manuals the lower is usually the choir, but sometimes combines choir and solo, the middle is the great, and the top is the swell. In organs which have four manuals the order is solo, swell, great, choir, the solo being at the top and the choir at the bottom. Compositions are mechanical contrivances for moving the stop-handles in groups at a time. The ordinary form consists of pedals, which project from the front just above the pedal keys. The arrangements are various. We may refer to the arrangement in the organ at Windsor, given later on. A species of composition was introduced by Willis some years ago, and has been adopted in many large English instruments, which acts by means of a series of brass disks placed just under the front of the keys of each manual, within reach of the thumb. These act by means of pneumatic levers. A slight pressure on one of the disks sets the machine attached to it in action, and the required change in the stops is made without any exertion on the part of the performer. The connexion between the keys and their pallets is made by various mechanisms, some of which are very ancient. In square and trackerwork (fig. 7) the old squares were made of wood. They resemble in function the squares used for taking bell-wires round a corner. The trackers are slight strips of wood, having screwed wires whipped on to their ends, which hold by leather buttons. The trackers play the part of the bell-wires. Where pressure has to be transmitted instead of a pull, thin but broad slips of wood are used, having pins stuck into their ends to keep them in their places. These are stickers (fig. 8). Backfalls (fig. 9) are narrow wooden levers turning on pins which pass through their centres. The fan frame (fig. 10) is a set of backfalls having one set of ends close together, usually corresponding to the keys ; the other ends are spread widely apart. The roller board (fig. 11) is a FIG. 7. A, square; B, tracker; more general mode of shift- metal square ing the movements sideways. The roller is a slip of wood, or a bit of metal tube, which turns on two pins inserted into its ends. It has two arms pro jecting at right angles toits length. One of these re ceives the pull at one point, the other gives it off at an- ~ n other. In case a FlG a ~ A aud B as iu fl - 7 c sticker - pull has to be transmitted to more than one quarter, a roller will sometimes have more than two arms. The name of couplers (fig. 1 2) is given to the mechanical stop by which the keys FlG - Backfall, of one manual are made to take down those of another, or those of the pedal to take down those of the manuals. Some old forms of the mechanism could not be put on while any of the keys Avere depressed; others had a tendency to throw the fingers off the keys. These forms have been entirely super seded. That now used consists of a series of backfalls centred on a movable support. The one set of ends is connected with the moving keys ; the other set of ends is pierced by the wires of the trackers or stickers from the * IG - io.-Fan frame, keys to be moved. In the one position of the support these ends play freely over the wires ; in the other they are brought up against the buttons of the trackers or against the stickers to be moved. The usual couplers are each of the manuals to the pedal, swell to great, swell to great octave, swell to great sub -octave, swell to choir, choir to great sub-octave, and solo to great. The swell oc tave and sub-octave couplers are sometimes placed on the swell itself. The objection to this is, that, if they are used when the swell is coupled to the great organ, as is very commonly the case, the octaves are reached through two couplers. And, as couplers are not generally screwed up quite tight, the FIG. 11. Roller board. FIG. 12. Coupler. octaves are often not sufficiently put down to sound in tune. The choir to great sub- octave coupler was used chiefly as a substitute for a double on the great organ. It is common in organs of the transition period, but is not a "rood arrangement.