386 NOTES PRODUCED BY TUBES. 



mouth, or between the lips and a leaf held close before 

 them, a sound may be produced which is caused in a 

 similar manner to that of the siren. The compressed 

 air forces its way out by slightly pushing aside the two 

 bodies; which, in consequence of their elasticity, in- 

 stantly return to their original position, and are im- 

 mediately afterwards again pushed back by the continu- 

 ous current of air; the same movement is repeated many 

 times in rapid succession; a series of impulses is thus 

 given to the air, and a note is produced. The move- 

 ment of the flexible bodies is, however, rather irregular: 

 the impulses do not follow each other at precisely equal 

 intervals of time ; hence the note is impure, of variable 

 pitch, and not pleasing to the ear. But if the soft bodies 

 are placed so as to close one end of a tube, which is 

 open at the other end, and air is blown between them 

 with suitable force, the column of air in the tube will 

 be made to vibrate, and its vibrations will determine the 

 rate of vibration of the flexible parts ; their motion is 

 thus made perfectly regular, and a pure, full, and 

 powerful tone is given out. The pitch of this tone 

 naturally depends, as in other tubes, upon the length of 

 the vibrating column of air. 



A pure and strong note may be produced, after a few 

 trials, by means of a tube of cardboard or, still better, 

 of glass, 2 cm wide and from 40 to 100 cm long, which is 

 held close to the lips, while a current of air is forced 

 from the mouth through the tube, the lips being 

 pressed together with moderate firmness. When the 

 lips are more compressed and the tube is rather long, 

 while the air is blown more vigorously through it, the 

 twelfth will be obtained besides the fundamental note, 



