182 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK n. 



briefly, the various parts of the mechanism by which the organist 

 obtains the musical effects peculiar to this wonderful instrument. 



The pufely instrumental or musical part of the organ com- 

 prehends an indefinite number of sonorous pipes which are grouped 

 in series, according to their tones in the musical scale ; each series 

 constitutes a stop or register, and the different pipes which compose a 

 stop are, as we shall see, distinguished by the pitch of the notes given 

 out by the lowest of each series according to their scale and length 

 when the wind from the bellows causes them to speak. Every organ- 

 stop, correctly speaking, is one of individual tone, and may resemble 

 any one of the particular instruments desired to be introduced into 

 the composition of the piece of music to be executed. The organist 

 can also use several stops at the same time by observing the laws 

 of harmony, according either .to his own inspirations or those of 

 the composer whose work he is performing. 



We will mention some organ-stops as they were constructed at 

 the end of the last century, pointing out that, besides their particular 

 names, others are given to them based on the maximum length of 

 the pipe commencing each series and producing the deepest note. 

 This length was expressed in feet. They are as follows : 



The double open diapason/of sixteen feet-tone, named in foreign 

 organs montre, because its pipes were mounted or placed in I he 

 front of the organ case ; the bourdon, a wooden-stopped pipe of 

 sixteen feet tone, ranging from two to three octaves ; the bombarde 

 or double reed, sixteen feet of zinc, tin or wood, is a reed-stop, the 

 preceding stops having flute mouthpieces. 



The diapason, or foundation-stops of the organ are generally in 

 metal of eight feet, and give the ground tone to the organ. 



The twelfth gives a fifth above the principal. 



The doublette or fifteenth is the octave above the principal 

 (consequently two feet). 



The larigot an octave above the twelfth. 



::T|i6# come tke stops, the cornet,: furniture, trumpet, then the vox 

 hjutnana, cremonaxjrrclarionette, clarion and the voix celeste. 



[.': These different stops are formed of pipes with various mouthpieces, 

 as-wellave already -stated, and of various lengths these lengths being 

 calculated <accprding :to the laws of vibration in open or closed pipes 

 ttt ille'/ tfae forms also vary. Wooden pipes are square or 



