CHAT. V.] 



777 K OHCAX. 



183 



three-sided, or formed like truncated pyramids with square bases ; 

 pipes of tin or an alloy formed partly of lead and tin are either 

 cylindrical or conical terminating in a point, or formed like a cone 

 widened out as a bell. Figure 118 shows the form of the bourdon of 

 sixteen feet, and that of the double open diapason of sixteen 'feet. In 



FIG. 134. Organ stops. 



1. Principal (4 feet). 2. Spitz-note (8 and 4 feet).-3. Twelfth (3 feet). 4. Cornet.-5. Flute (8 and 

 4 feet). 6. Trumpet (8 and 4 feet). 7. Vox humana (8 feet). 8. Bombarde, or double reed (16 and 

 8 feet). 9. Mixture (4 ranks). 



Figure 134 may be seen the forms of the pipes of some of the stops 

 just mentioned. There are open pipes, pipes quite closed, and lastly 

 pipes with a chimney, that is to say, partially closed. Stopped 

 wooden pipes are tuned by means of a wooden stopper covered with 

 leather which closes the aperture at top : by raising or depressing this 



