196 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK 11. 



tubes" and insulated metallic conductors (sixty-one in number), 

 which convey the electric current to the several -pallets of the wind- 

 chest. The great organ at Primrose Hill, London, therefore, affords 

 the most perfect example of the " composite " organ, partly mechanical 

 and partly electrical. Without the important aid of electricity, it 

 would not be possible to place mechanically an echo organ so 



Fio. 138. Barbari's organ, commonly called the Barbary organ. 



distant from the key-board. The large thirty-two-feet pedal pipes 

 and the thirty -two-feet bombard are severally supplied with wind by 

 independent pneumatic exhaust pallets, insuring promptness and 

 fulness of speech. 



In this organ, which may be taken as the example of modern 

 mechanical appliances, the French system of ventils has been aban- 

 doned as being unsuitable to the exigencies of the performer upon an 



