Organs designed for secular use are freely equipped with other means of making sounds than pipes. On a theatre instrument one may expect to find chimes, bird-whistle, xylophone, marimba, etc., in addition to drums, cymbal, triangle, castanets and many other "traps," as they are called, for the greater delectation of King Demos. Even in church organs of the United States 8ft. and 4ft. harps to the Choir and cathedral chimes to Great or Solo play an important part, and are by no means deemed out of place; whereas British practice, restrained by more sensitive church traditions, admits in this way nothing more fanciful than a tremu lant to the enclosed sections.
It but remains to add that wind is supplied to the organ by a form of rotary fan (not unlike a steam turbine), driven by an electric motor. From this fan the wind is conveyed in a zinc duct called a trunk to a junction-box, whence smaller trunks branch out to the reservoirs of each windchest. The dyna mo, generating current for the action, may be driven off the main motor by a "whittle-belt" and should be properly over-com pounded so as to maintain a steady voltage under varying loads. Gone are the proverbial bellows and still more proverbial "blow boy," save in remote country districts where there is no electric power; for they have long been ousted by these all-metal machines of greater endurance and fewer vagaries.
Compared to other pneumatic machines, the organ operates on a very light wind pressure. Seldom are even the most powerful reeds voiced on a wind exceeding the weight of 3o inches of water, while a large majority of stops speak on only 4-6 in. pressure.
Bedos de Celles, L'Art du facteur d'orgues (Paris, 1766-1778) ; Johann Gottlob Topfer, Die Orgel
; Arthur G. Hill, The Organs and Organ Cases of the Middle Ages and Renais sance (5883) ; Hopkins and Rimbault, The Organ, its History and Con struction (1877) ; John Wallace Goodrich, The Organ in France (Bos ton, U.S.A.) ; Ernest M. Skinner, The Modern Organ (Boston, 1917) ; G. A. Audsley, LL.D., The Art of Organ Building; F. E. Robertson, A Practical Treatise on Organ Building; Thomas Elliston, Organs and Tuning (4th ed. 1924) ; N. Bonavia-Hunt, Modern Organ Stops (1923) ; H. Heathcote Statham, The Organ and its Position in Musical Art (1909) ; Harvey Grace, The Complete Organist (192o). (D. B.-V_)