MUSIC AND SOUND INSTKUMENTS 



431 



piano by draw- 

 ing the air from 

 the mechanism. 

 The perforated 

 paper roll passes 

 across the tracker 

 bar which con- 

 sists of a series 

 of openings each 

 one of which cor- 

 responds to a 

 hammer or note 

 on the piano. 

 When a perfora- 

 tion in the paper 

 passes over the 

 opening the air 

 rushes in, causing 

 air pressure on 

 that part of the 

 piano which will 

 cause the ham- 

 mer to strike the 

 proper string. 

 The air pressure 

 is produced by 

 an air pump 

 (exhaust pump) 

 worked by the 

 feet. The harder 

 a person pumps, 

 the greater vac- 

 uum is created 

 behind the paper 

 roll passing over 

 the tracker. 



FIG. 321. Mechanism of a Piano Player. 



Courtesy of the Autopiano Company. 



