Page:The American Cyclopædia (1879) Volume XII.djvu/703

 ORGAN 689 of the added sonority and brilliancy ; and this is greatly facilitated by the pneumatic action hereafter described. The wind, having been collected and compressed, is conveyed to the several main divisions or departments of the organ by means of wooden tubes called wind trunks, and is received into the wind chests. The upper board of a wind chest is something like a chess board, with a pipe set above each square. Each row of pipes from right to left is controlled by a stop, within reach of the performer, and each row from front to back is controlled by a key. If there are 100 sound- ing stops, there will be from right to left 100 rows of pipes, with 100 perforated boards which slide under the pipes and admit or shut off the wind at the feet of the pipes. No pipe can speak until the drawing of a stop frees the holes at the bottom of the pipes, end a key being struck allows a supply of wind to rush in under the pipes. Each key con- trols its own separate air-tight compartment or wind reservoir in the wind chest, and each stop has one pipe over this compartment. In the case of mixture stops a cluster of several pipes takes the place of one pipe of an ordinary stop. Besides the stops and keys for the hands to play, there are in organs of the larger class two octaves and a half of large keys placed under the performer's feet, called pedals. There are also pedals and contrivances for moving num- bers of stops by one effort, and another pedal which opens and closes a box in which are the pipes of the swell organ. As this swell box opens, the sound is increased. There are also couplers for the different rows of keys. A coupler is an appliance by which one keyboard can be combined with another, or the same cla- vier can be united to itself in the octave above or below. The sound from each key as controlled by stops varies not only in quality but in pitch. If the stop drawn be a simple diapason, the sound which each key can give is the same in pitch as that obtained from a key occu- pying a similar position on the keyboard of a piano. If the stop be a double diapason, a tone is given an octave lower than that from a key similarly situated on the piano keyboard. If the stop is called a principal, the note is an octave higher ; if a fifteenth, two octaves high- er ; and if a mixture, a chord of several notes is given. Thus, by putting one finger on an organ key and by drawing six stops, several octaves of notes and a chord can be made to sound. In large organs of 100 stops, more, than 100 notes are played by simply pressing one key. Every sound in music gives out feebly in remote octaves every other note of the scale. (See HAEMONY.) When these tones, called harmonics, are strengthened judiciously, the result gives the effect of a strong unison note. When a single key is held and 100 stops are drawn, the ear cannot detect the octaves, twelfths, fifteenths, and even discordant inter- vals which give the strength, they being ab- sorbed in the foundation tone. Pipes are made of metal and wood. The chief varieties of metal pipes, as regards form, are the cylindri- cal, conical, conical surmounted by a bell, in- verted cone, and inverted cone surmounted by a bell ; while wood pipes are divided into four- sided, three-sided, cylindrical, pyramidal, and inverted pyramidal pipes. All pipes may be di- vided into two classes, flue pipes and reed pipes. Flue pipes are such as have an oblong opening, called the mouth, at the junction of the body with the foot of the pipe, bounded above and below by two edges called lips. These pipes are made to sound by the wind first passing through a narrow fissure called a flue or wind way, and they depend chiefly on the length or short- ness of their bodies for the gravity or acuteness of the sound they produce. Reed or tongue pipes are, on the contrary, those which are made to sound through the medium of a mouth- piece (not unlike that of a clarinet) furnished with an elastic plate of metal. Reed pipes do not depend on the length of the tube of the pipe but on the size of the mouthpiece and the vibrations of the tongue for the gravity or acuteness of the sound. The pitch of the sound produced by a reed pipe is determined by the number of beats or regular vibrations made by the tongue in a second of tune ; and the reeds are therefore made small or large according to the acuteness or gravity of the sound each is required to emit. The higher the pitch, the smaller must be the reed and the quicker the vibrations of its tongue. In a flue pipe the pitch is governed by the length of the body of the pipe, or more strictly speaking by the length of the column of air within it. By doubling the length the sound produced is an octave lower. The following table exhibits the number of vibrations which take place in a flue pipe, and the number of blows made by striking a reed in a second of time, in produ- cing the several C sounds used for organ-stop measurement, while to the right the shortened length of the pipe is given : NAME OF C. Vibrations in flue pipe. Blows of tongue in reed pipe. Length o( open fine pipe. C C C C. 82 16 82ft. C C C 64 82 16 " C C 128 64 8 Tenor C . 256 128 4 " Middle C 1 ... 512 256 2 " Treble C 1,024 512 1 " Organ pipes vary in size from a length of three fourths of an inch to one of 32 ft. The sub- ject of organ tuning is one of great practical importance as well as of scientific interest. In early times, before the invention of harmony, music for the church was written in simple form and without changes of key. The organ then was tuned upon a system of perfect at- tunement. When harmony was introduced and the semi-tones added, the system of unequal temperament was adopted, by which certain of the keys most in use were put in nearly perfect