drawn, into the reservoir (f
), in a continuous and equal stream, excess in which is obviated by a, discharge pallet (e
) acting as a safety valve. But when the expression-stop is drawn and the expression-hole (h
) to the reservoir is consequently closed, the air acts directly upon the vibrators or tongues (m
), from the feeders (c
). The entire apparatus for the wind is covered by the bellows-board (k
), containing the valves (j
) that admit the wind to the different rows of vibrators or reed compartments, as the stops (t
) may be drawn. Above the bellows-board is the 'pan' (l
), sometimes erroneously called the soundboard, a board of graduated thickness in which are the channels (n
)—separate chambers of air to each vibrator, determining, as said before, the different timbres
. The proportions of the channels and size of the pallet-holes are found empirically. The air within the channels, set in vibration by the tongues, is highly compressed. Sometimes, to gain space and a different quality, the channels with their tongues are placed upright. A stop (t
) being drawn and a key (q
) depressed, wind is admitted by the action to the tongue or vibrator, and escapes by the pallet-hole (o
)—at a comparatively even pressure if it comes from the reservoir, or at a varying pressure if, as already explained, the expression-stop is drawn and the wind comes from the feeders direct.
We give a cut of the percussion action already alluded to. Here q
is the key, which on being depressed sends down a 'plunger' (a
), which acts upon a little escapement action, with lever (b
), hammer (c
), and set-off (d
is the reed, which by this arrangement is struck by the hammer and assisted to move at the moment the wind is admitted.
The harmonium has a keyboard of five octaves at 8-ft. pitch.
The bass stops range up to and include the e on the first line of the treble stave; and the treble stops range from the f upwards—29 and 32 notes respectively—a wider compass than any other wind instrument. In an ordinary harmonium the registers or rows of vibrators are four in number, divided, as just stated, into bass and treble, and again into front and back organs as they are technically called. The front organ has the foundation and fuller toned stops, the back organ the imitation and more reedy stops. Thus, adding the French names as they are frequently to be met with—
Front. No. 1. Diapason bass and Diapason treble—Cor Anglais and Flûte. 8-ft. pitch.
No. 2. Bourdon bass and Double Diapason treble—Bourdon and Clarinette. 16ft. pitch.
Back. No. 3. Clarion bass and Principal treble—Clarion and Fifre. 4-ft. pitch.
No. 4. Bassoon bass and Oboe treble—Basson and Hautbois. 8-ft. pitch.
M. Mustel retains this arrangement of the foundation stops in all harmoniums; Mr. Bauer in large harmoniums has doubled them. In the large Mustel instruments other stops of great beauty are added, the indisputable introduction of their ingenious maker—
. Bass. 2-ft. pitch. Two ranks of