unshaded intermediate parts are the bearers, which sustain the weight of the upper-boards on which the pipes are seen standing, as well as of the pipes themselves; the sliders being thus left unfettered to move freely to and fro. In the small movable (Portative) organs of the middle ages, when the surface of the soundboard, or 'table' on which the pipes stood, was scarcely any higher above the keys than the top of a modern square pianoforte above its clavier, and when the soundboard measured only about a couple of feet in length, the slider-ends could be easily reached by the player, and be moved in or out with the fingers and thumb. When the soundboard became longer, and the sliders longer and heavier, a lever was added, to move them to and fro. This was the arrangement in the 16th-century organ at Radnor. At that period, and for a long time after, the stops were arranged before the playing commenced, and were not varied during the performance.
In a modern organ of what would now be considered small dimensions, the slider-ends are always beyond the reach of the performer, being, in relation to the claviers, generally farther in, considerably to the right or left, as the case may be, and at a much higher level. The 'action' to a single stop therefore consists of a draw-stop rod, which passes into the organ to the necessary extent; a movable trundle, which turns the corner; a trace-rod, which spans the distance from the trundle to the end of the soundboard; and the lever that is in connection at its upper end with the slider. These attached parts act in the following manner. The draw-stop rod is drawn forward in the direction from middle to front; the trundle partly revolves and moves the trace-rod in the direction from side to middle; and the lower end of the lever is drawn inwards, causing the upper end to move outwards, and to take the slider-end with it. The stop is now ready for use. On pushing in the draw-stop, the action of the several parts is reversed, and the stop is silenced.
The end of the draw-stop rod projects through the jamb at the side of the keys, and is finished off with a knob ornamented with an ivory shield bearing the name of the stop that it controls.
The Concussion-bellows was duly described under the head of Bellows (see vol. i. p. 216); it is only necessary therefore here to add that in the subjoined cut it is shown in position (see q) attached to the underside of the wind-chest.
Besides the two primary systems of mechanism just noticed, most organs, however small, have a greater or less number of members belonging to certain subsidiary systems, foremost among which rank the Couplers. Thus an organ with one Manual and separate Pedal generally has at the least one coupler, 'Manual to Pedal.' By means of this the lower 2½ octaves of the Manual are brought under the control of the feet, so that their sounds may materially supplement the Pedal stops, which are always moderate in number in email organs. [See Coupler, vol. i. p. 410.] A modern organ with two Manuals and separate Pedal has generally three, four, or even five couplers; 'Great to Pedal,' 'Swell to Pedal,' 'Swell to Great,' which is understood to act in the unison unless otherwise expressed; 'Swell octave,' which is understood to act in the octave above unless otherwise expressed. (It will be remembered that an octave-coupler formed part of the original work in Byfield's organ in St. Mary Redcliff, Bristol, 1726.) The 'Swell sub-octave' acts in the octave below. At first this was called a 'Double coupler,' as its effect resembled that of a 'Double diapason,' etc. In the organ built by Robson for St. Dunstan's in the West in 1834, there was a double coupler, Choir to Great, which operated by means of a second set of pallets, and therefore did not take down the Choir keys.
The 'action' of a manual-coupler of the modern improved kind consists simply of a set of levers or backfalls, one to each key. The front end of the backfall is lifted, the far end descending, and pressing down a sticker resting on the back end of the T-shaped backfall of the swell-action, which is then set in motion (g, h, i, i, k) as completely as though it had been started at f by the swell upper-manual key. An octave coupler consists of a set of diagonal backfalls, which extend sufficiently to the right to reach from any given key to the tracker of its octave. The upper backfall above h shows this. A sub-octave coupler has a set of diagonal backfalls acting on the octave below. When not required to be used, the drawstop is 'put in,' which raises the frame and backfalls from the stickers at the front end, and from the tracker-button at the other.
The Pedal-couplers are in modern examples made in manner similar to those just described, one of which may here be traced. On pressing down the pedal aa the trackers and roller-arms, bb, bb descend, drawing down the front end cc of the backfall. The far end dd is thus made to rise, lifting with it the sticker, which, communicating with the under-side of the tail (ee) of the great-organ key, lifts it and thus plays the note as exactly as though it had been pressed down by a finger.
The 'Sforzando coupler' is a movement worked by a pedal, by the aid of which the Great Organ is suddenly attached to the Swell. It reinforces the strength of the Swell to a far greater extent, and more quickly than by the 'crescendo' pedal; and is therefore useful when a quick and remarkable accent is required. It is formed of a backfall, the far end of which presses down a sticker resting on the back part of the square backfall of the Great Organ, which it depresses, and so sets the Great Organ tracker in motion. The first coupler of the kind was made by Lincoln, and introduced by him into his organ at St. Olave's, Southwark, erected in 1844. This coupler is always worked by a pedal, on pressing which the backfalls descend into position. On releasing the pedal the backfalls are raised from their work by a spring. Other subsidiary pedals are occasionally introduced, such as 'Great to Pedal, off or on, and 'Swell to Great, off or on.' These are of such constant use, that they ought to find a place in every organ of even moderate dimensions.
