Fig. 1 is a front view and Fig. 2 a side view of the wind-chest. A is the wind-chest into which compressed atmospheric air has been introduced, either through the side or bottom, from the end of the wind-trunk B. The pallets, C C C, are held against the openings, D D D, leading from the wind-chest to the mouth of the pipes, by springs underneath them.
Fig. 1. The Wind-chest. Front View
The spring S (Fig. 2) keeps the pallet C against the opening into D. The wires called pull-downs (P, P, P), which pass through small holes in the bottom of the wind-chest and are in connection with the keyboard, are attached to a loop of wire called the pallet-eye, fastened to the movable end of the pallet. A piece of wire is placed on each side of every pallet to steady it and keep it in the perpendicular during its ascent and descent, and every pallet is covered at top with soft leather, to make it fit closely and work quietly. When P is pulled down (Fig. 1) the pallet C descends, and air from the wind-chest A rushes through D into the pipe over it. But the slider f is a narrow strip of wood, so placed between the woodwork g and h that it may be moved backwards and forwards from right to left, and is pierced with holes corresponding throughout to those just under the pipes. If the apertures in the slider are under the pipes, the opening of a pallet will make a pipe speak; if, however, the slider has been moved so that the apertures do not correspond, even if the pallet be opened and the chest full of air from the trunks, no sound will be produced.
Fig. 2. The Wind-chest. Side View
When the apertures in the slider are under those below the pipe, the "stop," the handle of which controls the position of the slider, is said to be out, or drawn. When the apertures do not correspond, the stop is said to be in. Thus it is that when no stops are drawn no sound is produced, even although the wind-chest be full of air and the keys played upon.
This wind-chest with the slider stop control is about all that is left to us of the old form of key action. The pallets were connected to the keys by a series of levers, known as the tracker action.