192 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK n. 



pneumatic action. This mechanism consists in the use of a puff- 

 valve interposed between the key of the clavier and the valve before 

 mentioned. This puff- valve is put into communication with the 

 bellows by a wind-trunk, and a special valve, on which the key acts, 

 fills itself, and exercises a sufficient power to overcome the resistance 

 of the valve placed in the wind-chest, so that the force of the 

 organist's finger no longer exerts itself on the valve with a wide 

 surface, but on the small alimentary valve of the puff valve. 



This principle is also applied to the working of the registers and 

 the couplers, in order further to reduce the mechanical work of the 

 performer. 



FIG. 137.- Claviers of the great organ of Notre Dame in Paris. 



The number and variety of the stops have been also considerably 

 increased in organs recently constructed. 



The organ of Notre Dame possesses five manual claviers and one 

 pedal clavier. The pedal clavier generally extends from c to F, 

 and contains thirty notes ; and in modern organs each of the manual 

 claviers extends from c to c, five octaves, and possesses sixty-one 

 notes. 



Plate IX. represents the great organ, erected in a private music 

 room at Primrose Hill, with its magnificent 32-feet speaking front, 

 built by Bryceson Brothers ; and as this instrument is one of the 

 most modern and complete in its details and mechanism, a short 

 description is appended. 



