We now come to describe the appara tus which opens the valves, h, at the pro per time, to perform the note of a piece of music.
The axle, on which the crank, a, (fig. 1, 2, and 3) is formed, has an endless screw, o, (fig. 3,) cut upon it to turn a wheel, p, by the teeth cut in its circum ference; this wheel is in the same piece with a cylindric barrel, H H, shown se parately (in fig. 4, Plate II); it has a great number of short pins stuck in it, which as it revolves upon its pivots, catch the ends of a number of small levers call ed keys, r r r, and raise them; this de presses the other, t t t, ends, which are attached to the rods, G, and consequent ly open the valves. There are as many of the levers, or keys, as there are pipes, each answering to a different note of the gamut ; the pins in the barrel are so disposed, as to lift the keys in the same order and time as any piece of mu sic for which the barrel has been previ ously made. The keys all turn upon one wire, as a centre, and to prevent their shifting sideways ; and by that means missing the pins in the barrel intended for them, they move in small notches, cut by a saw in two pieces of brass plate, which are screwed to the edge of a piece of wood, K, and project below it ; the wire which forms the centre for the keys is also fixed to the piece of wood, K, which is called the key-frame. A num ber of small pieces of mahogany are fix ed to the keys at t, and to these the rods, G, are jointed by a piece of leather glued to both -o v, are small screws going through the key-frame, and touching the piece of wood, their use is to adjust the levers, so that the ends, r r, shall form one straight line.
The key-frame is not fastened down to the frame of the machine, but has a piece of iron plate, zo, fastened to each end, and turning upon screws fixed to the frame of the instrument, upon which the whole key-frame can be fitted as a centre ; two screws through its ends, resting their points upon the frame, support it, and by screwing these out, the whole frame can be raised or lowered, to adjust the ends of the keys the proper distance from the centre of the barrel, H.
By inspecting the plan and elevation, (fig. 1 and 3) it will be seen, that the barrel is longer than the set of keys, by the distance of one of the keys from the other; the barrel can be moved along endways this quantity, and for this pur puse it is mounted in a frame, (fig. 4) which slides in a groove, shown in the section (fig. 2); a small pin, P, (fig. 4) is fastened to the frame, and comes through the case of the instrument ; it has notch es cut in it, which receive the sharp edge of a bolt, L, (fig. 7) fixed there, and
which holds the barrel in any place it is set. By moving the barrel endways a short distance, an entire new set of pins is presented to the keys, r r, which pins are disposed differently to the former ones, and consequently play a different tune ; there are often five different sets, and as many notches, on the pin, P, (fig. 1.) Without some contrivance when the barrel is moved endways, its pins might catch some of the keys, and break or bend them : to avoid this, the bolt, P, which confines the barrel, and prevents it being moved either way, is held down by another bolt, R, (fig 7) sliding across the end of it ; this bolt has a pin fastened to the back of it, which goes through the case of the instrument, (marked x, fig. 2 and 3) and when drawn back, presses down the end of a lever y, the other end of which lifts up the key-frame, and thus raises the keys up clear of the pins in the barrel, before it can be moved endways to play another tune.
The regulator, D, is pressed down by two wire springs, which equalize the pressure upon the air contained in it, when, by the bellows forcing in more air than the pipes require, and conse quently it accumulates in the regula tor, it lifts up its lid, and the handle of a small valve, z, seen in the eleva tion, (fig. 1) is pushed against a part of the frame ; this opens the valves, and allows the air to escape, until the regula tor sinks by the action of the two wire springs.
From what we have said, a description of the operation of the instrument will be scarcely necessary. By turning the han dle, the crank, a, works the bellows, and supplies the air to the pipes ; the end less screw turns the barrel, and its pins lift up the keys at the proper time, opens the valves, and admits the air into the pipes. When soft music is to be played, the stop, m, (fig. 2) which has a handle coming through the case, is drawn out, and the other shoved in ; this stops the passages to the wooden pipes, and opens the metal ones ; for fuller music, the stop, m, is pushed in, and n drawn out ; the wooden pipes are then used, and, for very grand and loud music, both sets are used, by drawing out both stops, and when both are in the sound cases, though the handle is still turned. For changing the tune, the bolt, R, is drawn back, this raises the key-frame; the other bolt is then drawn back, and the pin, P, moved in or out to ano ther notch ; the bolts are then to be re turned. Several barrels are adapted to the same organ, to perform a great va riety of tunes.