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23. Much as to the nature of the mechanical structure of an organ must have been gathered from the historical sketch just given, but the following concise account will perhaps place the whole more clearly before the reader.

The most important fact to be first grasped is that an organ with independent pedals and two or more manuals is simply several organs of almost identical structure brought together so as to be conveniently under the control of one performer.
If then the mechanism from the key to the pipes is once explained, the same explanation will apply equally to each row of keys and to the separate pedal organ.
24. Let us start from the manual-keys, looking at Fig. 17 at each step.

Fig 17
Fig 17. (click for larger image)

A key is a lever, the front portion of which is exposed to view (a) Just behind the ornamental strip of wood forming a band between each manual is placed a weighted piece of wood lying on the whole length of keys from side to side, called the thumping board (b). Its duty is to keep the keys in position and resist any tendency they may have to rise unduly when released from pressure of the finger. Under the keys a series of pins are arranged on a piece of wood forming the pin-rail (c). These pins fit easily into holes in the keys and prevent them from oscillating when moving up and down. On the end of the key. and kept in position by a little pin running into a hole in the key, is the sticker (d). The upper end of the sticker has also a little pin which passes into the end of a horizontally placed lever called a backfall (e). At the other end of the backfall is a hole through which passes the lower end of a tracker (f). Trackers may be of various lengths according to the size and position of the instrument. The little wire passing from the end of the tracker into the hole in the backfall is made like a screw, or tapped, as it is termed ; so, where it appears below the backfall, a little leather button can be screwed on to it. Two purposes are answered by these buttons ; they prevent the tracker from jumping out of position, and they enable the builder to regulate the length of the tracker by twisting the button to the right or left If trackers are very long indeed, they are made to pass through one or more perforated pieces of wood, each tracker having one hole to pass through. These contrivances are called registers, and their object is to prevent the trackers from knocking against each other and making a rattling noise (g).
It will appear from the diagram that the upper end of the tracker is fastened to a pull-down (h) or piece of wire, one end of which passes out of a small hole in the wind-chest (i i), while the other is fastened to the bottom of the pallet (J). This has been purposely done to give the younger reader a general idea that the key pushes sticker, sticker raises front of backfall and at the same time forces down the further end of backfall, backfall pulls tracker, tracker pulls pull-down, pull-down pulls down (as its name implies) pallet, pallet allows wind to rush up to pipe.
25. But as a matter of fact the pipes are not arranged all of a row, beginning with the smallest on the right-hand side, ending with the largest at the left-hand side. If pipes were so arranged in large organs, not only would they present a very ugly appearance, but all the weight would rest on one side ; and also, as large pipes take much more room of course than little ones, the left-hand side of an organ would have to be of much greater depth. And again, if this arrangement of pipes were followed, the resources of the box of air, or wind- chest, would be taxed to the utmost on the left side where the big pipes were standing, while the other end would only have to supply tiny pipes. All these considerations have led organ-builders to place pipes alternately on either side, beginning with the largest. Thus—

C, D, E, F#, G#, A# , C, and so on, to the smallest, (Largest pipes on left-hand side.) ; then back again, ending C#, B, A, G, F, D#, C# . (Largest pipes on right-hand side.)
One is called the "C side," the other the "C# side." This accounts for the very unpleasant musical scale heard when a tuner is at work, because he tunes in this order on one side—
Music Stave

and in this order on the other
Music Stave

If the organ had a compass to or G3 the little pipes in the centre would stand thus-
. . . . C, D, E, F# G, F, D#, C# . . . .
The note G would be produced by the smallest pipe, and the pipes would gradually increase in size up to the largest—on the left side to the C of lowest pitch, on the right to the C# of lowest pitch.
26. It is evident then that as the pipes do not stand in the same order as the keys, that is, by successive semitones, the action of the trackers will have to move sideways also in order to get under their respective pull- downs. This sideways movement is managed by what is called a roller-board. A peep at a roller-board in an organ will show its use and construction far better than any amount of verbal explanation. But it will be easily understood that if a series of little rollers (of wood or thin iron) be placed horizontally on an upright board, having at one end a jutting arm fastened to the tracker, and at the other end a similar jutting arm connected with the pull-down, when the tracker pulls one end of the roller the other end of the roller will move the &qupt;pull-down,&qupt; and the pallet under the foot of the pipe will thus be opened.

27. Having shown how the movement of a key acts upon various levers until the pallet is pulled open.. our next step will be to trace the progress of the wind from the time it enters the bellows until it reaches the pipe: If the reader can understand these two processes, which always go on simultaneously, namely, leverage from a key and at the same time progress of wind from the bellows, he will have grasped the true principles of the construction of an organ.

The attentopn of the reader is now called to figure 18:-

Fig 18 (click for full size inage)
The bellows-handle, or whatever lever is employed in its place, moves the feeder (f g). Feeders are the lowest portion of the bellows, and are perforated with large holes (c c), closed inside by light coverings of leather hinged at one end (d d). When a feeder is moved down, the air from outside raises these light valves (d d) and fills it but as the return movement of the handle raises the feeder, the air cannot get outside again owing to the openings being covered up by which it entered; it therefore raises the valves in the reservoir (e e) above and enters in there. But the entry to the reservoir is closed by valves (e e) of similar construction to those which are placed in the bottom Of the feeder; as soon therefore as the air has got into the reservoir and the feeder begins to go down for the second time, the valves in the reservoir fall over the opening and the wind is secured inside the reservoir. On the top of the reservoir are weights (l I I l) carefully adjusted, which make the air try to get out through the trunk (k) at the side. These trunks are sometimes of metal, more usually of wood, and convey the air into the wind-chest. The trunk guiding the wind from the bellows will be seen at k in Fig. 18. The following (Fig. 19) shows the action of double feeders ; while one (a) is feeding the reservoir the other (b) is being refilled.

Fig 19

Fig 20

The junction of the wind-trunk to the wind-chest is shown by the dotted lines (b) in the next illustration (Fig. 20).
28. We have now traced the air into the wind-chest (a a a a in Fig. 20). It cannot go into the pipes at once because the pallets (c c c) stop the way.
When the action of the keys (just described on page 18) pulls down the pallets, the air makes a rush to get into the pipes through the grooves (d d d) ; and it will succeed in getting into the pipes if the slider (f) is open. The slider is a flat strip of thin wood which moves from left to right or vice versa, lying between the top of the wind-chest and the sound-board (g) in which the pipes (k I m) stand. The holes in the slider correspond exactly with the holes under the pipes. The slider is acted upon by the stop. When the stop is in, the slider is out of position and the air is arrested in its progress to the pipes by finding no orifice in the slider(f). But when the stop is out, the holes in the slider are under the holes leading to the pipes, and the air rushes into them and makes them speak. When, however, the key is allowed to return up to its position of rest, the pallet closes sharply and no more air car get to the pipes whether the stop is in or out.
29. As it is often found difficult to explain the action of the slider to young persons, the following way of stating it may be of use. Take three strips of paper, two of white, one of black. Place the black strip between the two white, so that they coincide. Make a few holes through all of them (Fig. 21) :—

Fig 21
Fig 21

Place them on a table. Then the lowest strip of paper represents the top of wind-chest, the black strip the slider, the top strip the sound-board and holes in which pipes stand. It will be evident that air could run through the holes in all the strips and enter the pipes if no further step be taken. But now take hold of the black paper and give it a little pull to the right. The following (Fig. 22) will be now the appearance on the table :—

Fig 22

It is very evident that, although there is an opening in the white papers, no pipe could now speak because the black paper stops the progress of the air. This is exactly the nature and function of the slider. The stop when out makes all the holes coincide, as in Fig. 21 ; the stop when in makes the slider intervene, as in Fig. 22.
Fig 23
Fig 23
In Fig. 20 (at c c c), the pallet was only shown from the front ; it will make its function clearer if we show it sideways, as in Fig. 23. The pulling of the wire opens the pallet, which is hinged at i, the air rushes therefore from a a into d d d, the groove. On releasing the key, the spring (s) instantly closes the pallet. The action which makes the stop-handle act on the slider is nothing more than a series of arms and levers ; and as it is a portion of the mechanism most easily visible when looking inside the instrument it is unnecessary to say more about it here.
30. Couplers are of two kinds, manual couplers and pedal couplers ; by the former, one of two rows of keys is so connected to another that when that one is being played the other also is acted upon at the same time; by the latter, when the feet are playing on the pedals the lower notes of a manual are simultaneously acted upon. The most simple couplers are
Fig 24
Fig 24
those which act upon one of two successive rows, such for instance as "Swell to Great," which signifies that when this stop is drawn and the Great Organ is being played the Swell is simultaneously acted upon. The coupler formerly most commonly used can be thus explained. The backs of the keys are cut away—that of the upper set at the under side, that of the lower at the upper side. A piece of wood is pierced with holes and made into a frame for the little flatheaded stickers shown at a and b. When the coupler is not drawn out the stickers are all at b, where they cannot produce any effect ; but when the coupler is drawn out the rod and all the stickers are thrown into position at a, and therefore upon pressing the front of the lower key the end rises and pushes up the back of the upper key. But backfall couplers, that is to say, couplers formed by the use of levers (such as that represented by e in Fig. 17, ), are now most frequently met with.
The following diagram (Fig. 25) shows both manual and pedal couplers on an organ of two manuals. Backfall couplers are placed out of gear (when the stop is in) by a displacement of the backfall frame in such a manner that
Fig 25
Fig 25 (click for larger image)
the wire of the sticker moves up and down without acting on the backfall. Pedal couplers, owing to the extent of the pedal-board being greater than that portion of the manuals on which they act, are constructed by means of a roller-board, or a backfall called a splay backfall, because the arms are not parallel to each other.
31. When couplers are drawn the touch of a large organ would be very heavy were it not for the pneumatic lever, for an explanation of which the reader is referred either to Hopkins's excellent work on the organ, or the article "Organ" in Stainer and Barrett's "Dictionary of Musical Terms."

32. The construction of all the flue-pipes in an organ can be gathered from an examination of Figs. 26
Fig 26
Fig 26
Fig 27
Fig 27
and 27 ; for, although they differ in detail in a vast number of ways, the principle remains the same. The air enters the foot (a) or lowest portion, is arrested by a piece of wood or metal (b) called respectively the block or languid (a corruption of the Latin lingua), is forced to escape in such a way as to impinge upon the lip (c), and thus sets the column of air contained in the pipe into vibration.

33. It is not an easy matter to explain the construction of a reed-pipe either by words or woodcuts. The student is recommended to ask an organ-tuner to take a reed-pipe to pieces and show how it is made. But to those who cannot thus see it with their own eyes, the easiest way to explain it, is to ask them to imagaine an ordinary clarinet with the reed end placed into a foot or boot so constructed that the bottom of the foot could be placed on an organ sound-board and the upper part should fit tightly round the portion of the instrument just above the reed. On the admission of the air from the bellows, it would have to pass by the reed of the clarinet to escape ; the reed would then by its elasticity beat against the orifice just behind it, and so be set into vibration.

Fig 28
DIAGRAM I (click for larger image)
The chests (a), (b), and (c) are charged with wind from the heavy-pressure bellows. On depressing the swell key the lever (e) opens the supply valve in the chest (a) and the spring (f) closes the exhaust valve (g), which allows wind to have access to the tubes (h) and the small chamber (i). The chamber (i) has two very sensitive diaphragms which, by the action of the compressed air, close the exhaust (j) and lift the supply valve (k), thus inflating the motor (i), which opens the pipe valve in wind-chest (m). The moment the key rises and opens the exhaust (g) the wind pressure in the chest (c) expels the wind from the chamber (i), which permits the lower diaphragm to exhaust the motor (l).
The coupling is accomplished by the slide block (n), on which are as many slides (o and p) as there are couplers on that manual. These slides are supported by springs and have an elongated cavity to each note, so that. when drawn, the main tubes (3) and (6) are coupled to the tube (4). The latter enters another air-tight chamber, the holes of which are guarded by small valves (5). When the Great key is depressed and the coupler drawn the valves (5) are blown over and prevent the wind from escaping through the exhaust valve (g), thus playing the Swell organ in addition to the Great organ.

Diagram III
(Click for larger image)
The pneumatic portion of this action is similar to Diagram ll., the automatic supply hole being between the two poles of the magnet (a). In a chamber below the magnet is the screwed seating tube (b), on the top of which—between guide pins—rests the small round armature (c). When the key is depressed the two wires (f) and (g) are connected by the pin (d), thus completing the electric circuit and causing the magnet (a) to attract the armature (c), by these means opening the tube (b) and closing the supply hole between the poles of the magnet. This causes the small motor (e) to collapse, and the movement is completed as in Diagram Il. On breaking the circuit by releasing the key, the armature is blown off the poles of the magnet on to the tube (b), which causes the motors to be re-inflated.

Extract:- Novelos Music Primer No3.
By J. Stainer
Edited by John E. West