This box must be made of thick stuff, say 1-1/2 inch deal; it will therefore be very heavy, and care must be taken to provide for its weight in planning the frame. It should be put together with screws, so that it can easily be taken to pieces for transit, and it is usual to line the whole of its interior with sheets of thick brown paper, applied with glue. It will be very convenient, if access can be had to the back of the organ, to fit the back of the box with hinged doors, or to make the back removable like a shutter; in this case the pipes should be planted so as to present themselves readily to the tuner. If access to the back cannot be had, then a space is inevitable in the middle of the organ for a passage-board, on which the tuner may stand, or at least place his foot, while he removes the front shades in order to reach the pipes planted accordingly. In the swell-boxes of church organs the sides of the box are generally fitted as doors; then, the pipes being planted with the tallest in the centre, diminishing in height to each end, half of them can be tuned at one operation. When the pipes are thus planted, the top of the box will slope towards each side from a central ridge, like the roof of a house.
We cannot doubt that many of our readers have had, or may have, opportunities of examining the construction of the shutters or shades of a swell-box. We have sketched it, however, in Fig. 50. The shades are 6 inches in breadth, and of the same thickness as the rest of the box, and each shade turns on pins let into the ends of it at a distance of 2 inches from its upper edge. These pins work in notches cut in the cheeks of the box, so formed that any shade may be easily lifted out and replaced. The edges of the shades are bevelled to half a right angle so that they overlap when closed, and the bevelled surfaces are faced with leather or cloth to shut in the sound more effectually.
The mode of opening the shades, and so producing a _crescendo_, is shown in Fig. 51. _a_, _b_, _c_ are arms of oak, morticed into the shades at the level of the pins, viz. 2 inches from the upper line; _d e_ is a long rod or tringle of wood, connecting all these arms by pins passing through them and itself. It is evident that by drawing up this rod at its top, or by pushing it up from below, we shall open all the shades at once, and as they are hung on axes placed at one-third of their breadth, they will close by their own weight when released. The leverage by which this movement is brought under the control of the player may be safely left to the inventive powers of the reader. It is usual to give promptness to the return of the swell-pedal, and therefore to the closing of the shades, by attaching a strong spiral spring to the pedal, and to some firm point in the frame.