Part 18 (2/2)

WHERE OVERTONES ARE USED

In the flute, piccolo, and clarionet, as well as in the horn class of instrument, the overtones are as i the length of the column of air, the fundamental notes are also altered, while the har the blowing pressure; so that a continuous chrohout the compass of the instrument

THE ORGAN

From the theory of acoustics[30] we pass to the practical application, and concentrate our attention upon the grandest of all wind instruan This mechanism has a separate pipe for every note, properly proportioned A section of an ordinary wooden pipe is given in Fig 138 Wind rushes up through the foot of the pipe into a little chamber, closed by a block of wood or a plate except for a narrow slit, which directs it against the sharp lip A, and causes a fluttering, the proper pulse of which is converted by the air-column above into a musical sound

[Illustration: FIG 138--Section of an ordinary wooden ”flue” pipe]

In even the sans more than one pipe is actuated by one key on the keyboard, for not only do pipes of different shapes give different qualities of tone, but it is found desirable to have ranks of pipes with their bottoth of an open pipe is e of the lip to the top of the pipe; of a stopped pipe, froain When we speak of a 16 or 8 foot rank, or stop, we mean one of which the lowest note in the rank is that produced by a 16 or 8 foot open pipe, or their stopped equivalents (8 or 4 foot) In a big organ we find 32, 16, 8, 4, and 2 foot stops, and some of these repeated a number of times in pipes of different shape and construction

THE ARRANGEMENT OF THE PIPES

We will now study briefly the an, with five ranks of pipes, or stops

[Illustration: FIG 139--The table of a sound-board]

It is necessary to arrangedown of one keyto it speak, or only four, three, two, or one, as we may desire The pipes are mounted in rows on a _sound-board_, which is built up in several layers At the top is the _upper board_; below it come the _sliders_, one for each stop; and underneath that the _table_ In Fig 139 we see part of the table from below Across the under side are fastened parallel bars with spaces (shown black) left between theroove is enclosed by wood at the top and on all sides The under side of the table has sheets of leather glued or otherwise attached to it in such a roove to the next Upper board, sliders, and table are pierced with rows of holes, to perrooves under the big pipes are wider than those under the small pipes, as they have to pass rooves also vary in width according to the weight of the pipes which they have to carry The sliders can be moved in and out a short distance in the direction of the axis of the rows of pipes There is one slider under each row When a slider is in, the holes in it do not correspond with those in the table and upper board, so that no wind can get fro 140 shows the manner in which the sliders are operated by the little knobs (also called stops) projecting froan within convenient reach of the performer's hands One stop is in, the other drawn out

[Illustration: FIG 140]

In Fig 141 we see the table, etc, in cross section, with a slider out, putting the pipes of its rank in coraular _pallets_ which adives us an end section of table, sliders, and wind-chest, together with the rods, etc, connecting the key to its pallet When the key is depressed, the _sticker_ (a slight wooden rod) is pushed up This rocks a _backfall_, or pivoted lever, to which is attached the _pulldown_, a wire penetrating the bottom of the wind-chest to the pallet As soon as the pallet opens, wind rushes into the groove above through the aperture in the leather bottom, and thence to any one of the pipes of which the slider has been drawn out (The sliders in Fig 142 are solid black) It is evident that if the sound-board is sufficiently deep from back to front, any number of rows of pipes may be placed on it

[Illustration: FIG 141]

PEDALS

The organ pedals are connected to the pallets by an action sienerally of deep tone, 32-foot and 16-foot, as they have to sustain the bass part of the musical harmonies By means of _couplers_ one or more of the keyboard stops may be linked to the pedals

SEPARATE SOUND-BOARDS

The keyboard of a very large organ has as many as five _manuals_, or rows of keys Each an mounted on its own sound-board

[Illustration: FIG 142]

[Illustration: FIG 143--General section of a two-ed in steps, each slightly overhanging that below Taken in order froan_, of stops of small scale and very soft tone, enclosed in a ”swell-box” (2) _Solo organ_, of stops i orchestral instrus to this an_, contained in a swell-box, the front and sides of which have shutters which can be opened and closed by the pressure of the foot on a lever, so as to regulate the a fro pipes of powerful tone (5) _Choir organ_, of soft, mellow stops, often enclosed in a swell-box We an_, which can be coupled to any but the echo manual