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.
There were usually six joints or sources of friction, between the key and the pallet. To overcome this resistance and close the pallet required a strong spring. Inasmuch as it would never do to put all the large pipes (because of their weight) at one end of the wind-chest, they were usually divided between the two ends and it became necessary to transfer the pull of the keys sideways, which was done by a series of rollers called the roller-board. This, of course, increased the friction and necessitated the use of a still stronger spring. That with the increased area of the pallet is why the lower notes of the organ were so hard to play. And to the resistance of the spring must also be added the resistance of the wind-pressure, which increased with every stop drawn. When the organ was a large one with many stops, and the keyboards were coupled together, it required considerable exertion to bring out the full power of the instrument; sometimes the organist had to stand on the pedals and throw the weight of his body on the keys to get a big chord. All kinds of schemes were tried to lighten the "touch," as the required pressure on the keys is called, the most successful of which was dividing the pallet into two parts which admitted a small quantity of wind to enter the groove and release the pressure before the pallet was fully opened; but even on the best of organs the performance of music played with ease upon modern instruments was absolutely impossible.
CHAPTER III.
THE DAWN OF A NEW ERA—THE PNEUMATIC LEVER.
Just as we no longer see four men tugging at the steering wheel of an ocean steamer, the intervention of the steam steering gear rendering the use of so much physical force unnecessary, so it now occurred to an organ-builder in the city of Bath, England, named Charles Spachman Barker,[1] to enlist the force of the organ wind itself to overcome the resistance of the pallets in the wind-chest. This contrivance is known as the pneumatic lever, and consists of a toy bellows about nine inches long, inserted in the middle of the key action. The exertion of depressing the key is now reduced to the small amount of force required to open a valve, half an inch in width, which admits wind to the bellows. The bellows, being expanded by the wind, pulls down the pallet in the wind-chest; the bellows does all the hard work. The drawing on the next page, which shows the lever as improved by the eminent English organ-builder, Henry Willis, shows the cycle of operation.
When either the finger or foot is pressed upon a key connected with k, the outer end of the back-fall gg is pulled down, which opens the pallet p. The compressed air in a then rushes through the groove bb into the bellows cc, which rises and lifts with it all the action attached to it by l. As the top of the bellows cc rises, it lifts up the throttle-valve d (regulated by the wire m) which prevents the ingress of any more compressed air by bb. But the action of the key on gg, which opened the pallet p, also allowed the double-acting waste-valve e to close, and the tape f hangs loose. The compressed air, therefore, as it is admitted through bb cannot escape, but on the other hand when the key releases the outer end of g, and lets it rise up again, the tape f becomes tightened and opens the waste-valve, the bellows cc then drops into its closed position.
