184 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK n. 



more or less into the bod} 7 of the pipe the length of the vibrating 

 column is modified. Metal pipes were often tuned by using flexible 

 metal plates soldered on each side of the mouth ; these movable 

 plates, called ears, could be pressed closer or pulled more open, and 

 so flatten or raise the pitch of the pipe by influence on the freedom 

 of the stream of air escaping at the mouth. 



The system of ears for tuning purposes is now out of date. 

 Lastly, the reed-pipes are tuned by using the tuning-wire to press 

 the metal tongue against the aperture, and thereby to extend or 

 shorten its vibrating length. 



These stops as a rule extend to the same compass on the musical 

 scale, or rather are composed of an equal number of pipes each pro- 

 ducing one of the notes of the scale. For instance, beginning with 

 the diapason which in modern organs embraces five octaves from cc 

 to c in altissimo, three high and two low ; the principal, twelfth, 

 fifteenth, flute, clarion and voix celeste have the same compass. All 

 the cornets, grand cornet, and echo- cornet in all modern examples, 

 each have a compass of five octaves. The vox humana, cremona, 

 trumpet and bourdon give five octaves ; the large open diapason and 

 sixteen foot bourdon comprise five octaves. 



The stops we have just spoken of belong to the organs built to- 

 wards the end of the last century. By adding to them five pedal 

 stops, we have thirty different stops to a complete organ. The number 

 has been increased since. The organ at Haarlem, though now by no 

 means approaching in size instruments of modern construction, is 

 one of the most famous organs ; it has 60 stops and 4,088 pipes. 

 Many organs of more modern construction* number considerably 

 more stops, sometimes reaching 100 in number. The organs at 

 Liverpool, Dim, Saint Sulpice, Albert Hall, with other English 

 instruments exceed 100 stops. 



