Page:Popular Science Monthly Volume 40.djvu/660

640 to—working them by the feet, the blowers holding on. to a rigid transverse bar as they moved along the row (the bellows described by the authority named numbered twenty, and were operated by two men)—was, however, known a thousand years previous, in Constantinople. Passing over incidental contributions to that department, it is only necessary to point out that the demands upon the wind became so great in time that it was deemed necessary to introduce mechanical means for supplying and regulating the supply required. A hydraulic engine, invented by Joy and Holt, of Middleborough, England, though defective in some respects, was the first thing found to answer the purpose. Next came a water-moter, invented by Thomas Duncan, which met with some favor. Latterly, gas and electricity have been applied with much success, and in the operation of the most comprehensive organs little difficulty is experienced at present in supplying and regulating the stock of wind required.

When the organ-builder increased the compass of the instrument and its effects, the perfecting of the key movement, the invention of the draw-stop action for controlling the use of the various tiers of pipes, the introduction of composition pedals, couplers, and other features became necessary as a part of the major development, viz., the modern great organ as it stands. Of electricity and pneumatics nothing more need be said save that these agencies have been found invaluable in operating massive instruments.

A description of the Tabernacle organ in Brooklyn will show the mechanical and scientific points of interest contained in a modern instrument of that class: The great-organ key-board (A) is capable of controlling all the others—namely, swell (B), choir (C), and solo organ (D). In effect, the great-organ keyboard through the tracker (A) and squares (A) opens the ports of the pneumatic chest (E), the interior of one of which is shown. This is filled with compressed air of a power and quantity capable of raising a column of water seven inches. When the key is pressed, or operated, it opens the vent-valve (G) and closes the supply-valve (H). The compressed air from the chest presses on the top of the small bellows (I), one of which is furnished to each note, and the wind, consequently escaping through the vent-valve, pulls the wire of lever (J) and tracker (J). This passes up and pulls open the big valve in the great-organ wind chest, and affects all the other organs also, when coupled on to the tracker indicated.

To explain the action of the choir key-board (C): On being pressed, the key (C) opens the train of trackers and connections (K); the vent-valve (L) in that chest is opened, which closes the supply-valve (N), thereby allowing wind to escape from the small