SYNTHESIS OF VIBRATIONS. 



133 



to add another vibrating reed with magnet to the end of the first one 

 (see "Elements of Experimental Phonetics," p. 70), but the additional 



weight on the end of the spring made 

 the apparatus difficult to manage; 

 a multiple pendulum was therefore 

 tried. 



The multiple pendulum is shown 

 in figure 119. The frame carries a 

 projecting half circle with bearings 

 for the knife edges of the longest pen- 

 dulum. This pendulum is held bj' a 

 screw in a metal block; the posi- 

 tion of its point of support may be 

 adjusted, or it can be replaced by a 

 shorter pendulum; in this way its 

 period may be varied. It carries an 

 adjustable half ring with bearings 

 for the knife edges of the second 

 pendulum. The second pendulum is 

 held in a similar metal block with 

 knife edges; it carries an adjustable 

 bearing for the third pendulum, etc. 

 In this way the vibrations of three 

 pendulums may be compounded and 

 the period of each may be varied 

 at will. The pendulums are set in 

 motion by a sharp blow from a 

 felt hammer, or by a puff of air; 

 these blows are repeated at inter- 

 vals. The period of the blows and 

 those of the pendulums can be 

 varied at will. The sharp blows 

 represent the glottal puffs and the 

 various pendulums the vibratory- 

 elements of the vocal cavity. Vari- 

 ous degrees of friction are introduced by adding wind vanes to the 

 pendulums. The principle is capable of extension to more than three 

 pendulums. 



If the vowel vibrations are the results of puffs of various sharpness 

 acting on a series of cavities, the analogy of this apparatus to the vocal 

 vibrator}' system is verv close It must be possible to obtain curves that 



Fig. 119. — Multiple pendulum. 



