168 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK ji. 



be set in vibration, and this is accomplished by conveying a vibratory 

 movement to one portion of it, generally at one of its extremities 

 furnished with an appendage or mouthpiece which facilitates the set- 

 ting up of this vibration. As a rule, it is by insufflation produced by 

 the lips of the performer, or by mechanical means, that the vibra- 

 tions are produced and communicated to the air contained in the 

 instrument. Hence the name wind instrument. 



These instruments are very varied in form, dimensions, and 

 mechanism : some are constructed of wood, others of metal and 

 even glass or crystal. But the most rational classification is that 

 which distinguishes them by the special mouthpiece appropriate to 

 each. We shall thus find musical instruments with flute mouth- 

 pieces : these are represented by the flute itself and the organ pipes, 

 which were employed in studying the vibrations of gaseous columns 

 in the Forces of Nature ; then come instruments with beating 

 or striking and free reeds ; the clarionet and hautboy are the two 

 principal types of this series: lastly, wind instruments with that kind 

 of mouthpiece employed in the horn, trumpet, and most other brass 

 instruments. 



I. INSTRUMENTS WITH FLUTE MOUTHPIECES THE FLAGEOLET, 

 FLUTE, AND FIFE. 



Fig. 115 shows how the flute mouthpiece is formed, and how the 

 vibrations of the column of air are produced by breathing or causing 

 a current of air to pass over it. The breath or current, of air pro- 

 duced by the bellows strikes against the bevelled sides, and divides 

 into two currents, one of which acts on the interior column of air 

 and puts it into vibration : l the vibration being the result of the 

 successive compressions and reflexions of the strata of air on the 

 edge of the bevelling. 



We must not forget that if a vibratory movement is given to the 

 column of air inclosed in pipes with a section small relatively to the 

 length, the sounds produced will have a pitch inversely proportional 



1 Mr. Baillie Hamilton considers it doubtful whether the current is thus " split " 

 on the top. He considers that it rather glances off externally, in a continuous 

 stream, producing an aero-plastic " reed," in addition to its other functions of 

 rarefying, &c. 



