132 THE STUDY OF SPEECH CURVES. 



When a single sharp electric impulse is sent through the magnet 

 while the damper is out of contact, the spring vibrates for a long time. 

 When the damper is applied, the same impulse produces a vibration whose 

 amplitude steadily decreases; the rate of decrease depends on the degree 

 of friction. Three specimen curves with increasing degrees of friction 

 are shown in figure 117; the ampUtude steadily decreases in each case, 

 but more rapidly as the friction is greater. Such curves represent approxi- 

 mately the equation of the frictional sinusoid, discussed above (p. 104). 

 From the values of successive amplitudes in the same curve the degree 

 of friction can be calculated (p. 106). The sharp electric impulse represents 

 the glottal puff, the vibrating spring with much friction represents the 

 vocal resonance with its poorly reflecting walls (p. 110). If such an appa- 

 ratus can be made to produce curves resembling the vowel curves, it 

 furnishes proof of the correctness of the puff theory of vocal action. 



The curve in figure 118 looks like the curve of an initial vowel with 

 some of the minor irregularities smoothed off; in fact, it is the type of an 

 initial vowel curve after elimination of the pecuharities due to the specific 

 vowels. It was made by a series of magnetic impulses acting on the 

 spring, the impulses being at first far apart and then gradually closer. 

 While the impulses are far apart, the vibration of the spring from each 

 impulse dies away and is followed by a straight line; as the impulses 

 come faster the vibration for one has not time to die away and its effect 

 is united to the following one. A little later the period of the impulses 

 approaches more nearly the period of the spring and a resonance effect 

 begins to show itself. This is exactly the case with the action of the 

 glottal puffs on the largest element of the vocal cavity in the initial vowel. 

 It is also possible to obtain curves like those for [i] and [u] in the 

 Depew plate by using a contact apparatus (described in " Elements of 

 Experimental Phonetics," Chapter I), and adjusting the period of the 

 contact to an octave below that of the spring; the minor fluctuations and 

 deformations of the vowel curves — due to the higher tones— are lacking in 

 these curves, but to the eye they often appear exactly like vowel curves. 

 That such close similarities to vowel curves can be obtained from a 

 single vibrating spring is due to the shortness of the magnetic impulse 

 (whereby the suddenness of the glottal puff is counterfeited), to the high 

 degree of friction (as in the vocal cavity), and to the fact that all vowels 

 contain one very strong cavity tone in comparison with which the other 

 tones do not show prominently in the curve. 



This apparatus is adapted to the study of the general vowel type of 

 vocal action under variations in the suddenness and pitch of the glottal 

 puffs and in the change of the main vocal cavity. The attempt was made 



