According to strict rule the pull-downs, passing through holes in brass, should themselves be of iron or steel; but we have always used brass wire, and we must refer our readers to what we have said of this material in treating of springs. They must judge for themselves. The essential thing is that the wires should play easily and smoothly through the holes, drawing down the pallets with perfect freedom, and allowing them to return, when released, with a pleasant smartness. If a single pull-down fails in these respects remove it at once. Perhaps it is a little bent or bruised; possibly the hole in the plate may have been inadvertently left with a sharp edge, which has cut a notch in the wire; possibly, also, the pallet-ring may not be quite in a line with its fellows, and therefore not quite correctly above the hole in the plate, throwing the pull-down out of a right line into an oblique one. Rectify all defects of this kind at any expenditure of time and patience.
We have left all this time several inches of each channel open or uncovered, since the wind-chest closes in only that portion of the channels to which the pallets are applied. We may now finish our work by gluing white leather, or parchment, or even only stout paper, over the open part of the channels, taking care that it adheres well in every part.
We may add that it is sometimes, or often, convenient to place the wind-chest under the back part of the sound-board, and not under the front; or to place it midway between the back and front, or a few inches from either. This is done with an eye to arrangements connected with the action or movement, which will be described in detail. When the wind-chest is so placed care must be taken to provide for the complete closing of the front board. A ledge of wood should be glued and pinned to the bars in such case, to afford a bearing for the front board and to receive the screws which secure it; or the edges of the board may be leathered, and it may be thrust in, with a tight fit, between the under side of the channels (roofed with wood at that point for the purpose), the cheeks, and the bottom board, cut an inch wider accordingly. Wedges are sometimes used, driven in behind clasps or hooks of iron, to keep it in its place. But in truth, when the organ is once well built and finished, several years may elapse without a disturbance of the board.
CHAPTER VI.
THE BELLOWS, TRUNKS, AND FRAME.
After all our minute operations with small drills and fine wires, calling for a light hand and patient accuracy, we have to turn to work comparatively rough and coarse. The business of bellows-making presents no serious difficulty, and we hope we may pass rapidly over it. We shall have no reader who is not already familiar with the form of organ-bellows, which consist of three main boards, namely, the middle board, the top board or table, and the feeder, and of thin plates of wood called ribs, the whole united together with flexible white leather forming hinges and gussets.
The shape or form of the bellows will of course be determined by that of the organ; they may be long and narrow, or short and wide, like the sound-board. Their capacity, or area, will depend on the number and character of the pipes which they have to supply with wind. A common rule is to assign two square feet of superficial area for each stop in the organ; but this would be in excess of the requirements of such a small organ as that which we are making. 3 feet 6 inches by 2 feet, giving 7 square feet of area, will be ample dimensions in our case, and will work in conveniently with the size which we have assumed throughout for the sound-board, namely, about 4 feet or 4 feet 6 inches by 15 inches. In arranging your plans in the first instance, allow room for a drop or play of the feeder of at least 10 inches, free of all interruption from the pedal or other contrivance for blowing, for it is upon the capacity of the feeder that you must depend for the quantity of air supplied, the upper part of the bellows being merely a reservoir in which the compressed air is stored away, and from which it is distributed to the pipes as it is wanted. The reservoir may have a rise or play of about 10 inches or a foot. Get out the three main boards of deal or any sound stuff, leaving the middle board some inches longer than the other two, that its ends may rest upon the frame of the organ, or upon other supports as you may arrange. Cut out pieces, also, to form a shallow box, say 4 inches deep, upon the middle board, of the same size as the top board. This is called a trunk-band, and is introduced to allow of fixing the wind-trunks which are to convey the wind to the chest. You will want also a light frame of three-quarters stuff, pine recommended, to carry and support the ribs of the reservoir; the four boards of which it is made will be of the same width as the ribs themselves, namely, about 4 or 4½ inches. The ribs are of very thin stuff, say ¼ inch, but they must be quite sound and free from cracks. You will want sixteen ribs (eight pairs) for the reservoir and six for the feeder; of these last the long ones will be of triangular form.
