THE STOPS. Each stop include, a number of pipes which follow each other chromatically and extent! over the entire keyboard or some portion of it. Each set of pipes consists of tubes producing the same quality of tone through out ; thus the (;erman term Ntinunc ( voice) for stop is singidarly appropriate. Stops are classi fied as ( a ) complete stops. 1L1 ineomplet e Mops. (e) -.bort stops, (d) divided stops. (e) eompound stops. Complete stops extend the entire length of the keyboard: incomplete stops do not do so. Short stops are those which can not he eompleted by any other ,top. Divided stops are those which divide the manual compass hetlwccll them. Compound stops have two or more to a note, ( see AltxruaE.) The t one qualifies of the pipes of an organ may be classified as follows: The organ tone, which is best represented by the English lfi-foot and S-foot open diapason octave works: the German Ii1-foots 8-foot. and 4-foot principle: and the French 8-foot montre. and 4-foot taut : the Thar tone by the let-foot Bourdon, 8-foot stopped diapason. Gedeekt. Afolodia. Clarabella. and the y•foot and 4-foot flutes: the string tone by the I fi-foot pedal l'iOlone. contra gamba. S-foot violin. 'cello. gamba. keraulophon, viol d'amour: the reed tone by the trumpet, oboe. bassoon. clarinet. vox humana, trombone, etc. The structure of organ pipes consists of two general classes, viz. flue and reed pipes. The former derive their name from the method by which their tone is produced, i.e. the passing of air from the foot of the pipe through a flue, or narrow opening. across the month of the pipe. Such pipes are made of metal and wood. If of drieal; stopped rectangular; and half-stopped rectangular.
Reed pipes are of two kinds—the striking or impinging reed. in which the vibrator strikes a:Za hist the reed or metal tube inserted in the block of metal which fits into the boot of the pipe, and the free reed which in vibrating passes in and out of the opening freely and without touching o• striking. This latter species, how ever, is seldom used With the impinging reed the vibrating portion of the tongue may be lengthened or shortened, and made to vibrate slower or faster by raking or lowering the tuning spring, and thus bringing it to the desired pitch. In the case of the free reed, the tongue vibrates in the opening on the face of the eschallott. Sometimes the tuning is regulated by thumb-knots on a threaded wire. Reed pipes are either of metal or wood; in the turner ease their shape is either inverted conical, the same surmounted with a bell. cylindrical, the same surmounted with a hell, conical, or cylindrical half stopped. Witb the lowest toned reeds the pipes are usually of wood, four-sided. and in some organs are thirty-two feet in length. Free reed pipes have their bodies usually made of wood. The peculiar quality of the reed tone is largely caused by the presence of harmonics, and is due chiefly to the curve of the tongue, and the scaling and length of the tube. As in the case of flues, reed pipes are occasionally made of double or half length. It was stated earlier in this article that the reeds were peculiarly French and that the Germans were strongly inclined to the flues. Locher speaks of this as nationally chyrac•teristic, and gives the two fol lowing examples: The Alfinster organ in Ulm (Walcker), as compared to the organ of the Trocadero Palace, Paris (Cavan ; and the organ of Saint Johanniskirche, Stuttgart (Weigle), as compared to the _.Minster organ, Geneva (Alerklin). An ancient family name for such reed stops as the Geigenregal and the Jung Fernregal is 'Regals,' which is still sometimes used.
The parts of the organ naturally fall into three divisions: the pipework, the mechanism for blowing (bellows, channels, wind chest, etc.), and the mechanism by which the wind is utilized. The pipes are arranged according to the stops to which they answer. Each pipe gives but one
sound, so that the number of pipes must equal the number of sounds required, and if there is but one stop on the organ, there would have to he as many pipes as there are keys on the clavier. The pipes of each register are so placed that they can all at the same time be connected or shut off together by the action of the -top. The pulling out of a stop admits the wind to the chest, so that it is only necessary to press the key, which in its turn opens a small valve. to voice the pipe belonging to that key. The various manuals are connected together by couplers, manual and pedal. The frame ordi narily unites the manuals with the great organ, but in all large organs and the most recent small organs the manuals may be coupled among themselves; besides these there are the octave couplers, which unite every key with that of the upper or under octave. or both. in which latter case it is generally called the double octave coupler. This coupler produces an ex ceedingly full tone. When we speak of pneumatic action we mean the mechanism which is used to operate the pallets,- and stops and their mov ing mechanism, the motive power being com pressed air or atmospheric pressure rushing in to fill the vacuum. In every case the motor is a bellows. i.e. a device for general wind. and of an extensible nr collapsible design. :Motors may be either near the keyboard transmitting their power in the desired direction by means of a long tracker, or they may be situated near the part upon which they net. in which case they are governed by other small motor: situated near the keys and omnected with the large motors by small tubes of indefinite length. la the first instance the transmission of power is by trackers, but in the latter instance it is by what is called tubular• pneumatics. In the tubular pneumatic system the position of the motors inside of the Wind chest enables the pressure of the wind, when the key is at rest, to have access also to the interior. of the motor, so that the top is balanced bt• the pressure of the wind within and without. The ordinary pneumatic lever action mar be said to work on the principle of the inflation of a feeder or motor. In this action the pressure of wind, or the size of the motor, must be so arranged as to be of sufficient power to draw the aeth.n attached to that portion of the motor whieli is free to move win]) the inflation take: place. While this action is exceedingly useful for large instrument., in which the cOniplicated mechan km makes the touch too heavy for comfortable playing. it nevertheless lacks the exact precision of attack, and is fatal to correct phrasing and touch, in that there is no sharp edge to the cessation of tone. Tubular pneumatics. on the other band, have been found to give a very prompt tone in pedal work, owing to the fact that the pallets instead of being hinged may open and close in parallel motion. If well made, this action will not easily get out of order, besides which it appeals to the player in that it lends itself easily to octave work. Its expense, however, is a serious item, owing to the weight and cost of the tithing and necessary apparatus. Elec•tro-pneuniatic actions, which are, as their name implies, a combination of electrics and pneumatics, have thus far satisfied all require ments except perhaps that of absolute reliability, although the advocates of the principle assert that that fault has been overcome. In this action a tiny disk valve is opened by electricity and admits the heavy pressure wind to the pneumatic movement near the pallet. The console or key board. through the various mechanical and elec trical actions. may be placed in any position eon venicot to the player, quite independent of the location of the instrument. Numerous mechani cal aids to registration are also important features of the modern organ.