SCIENTIFIC RESEARCH APPLIED TO THE TELEPHONE 255 



toward the loudness of speech. As the sound wave produced by 

 speaking this sentence travels along, each particle of air over which it 

 passes executes a vibration through its original or undisturbed position. 

 The successive positions occupied by the particle as it moves in the 

 complicated series of vibrations corresponding to a spoken sound can 

 be visualized in laboratory investigations from oscillographic records 

 of the corresponding telephone currents. 



Each successive particle of air along the line in which the sound is 

 traveling executes a similar complicated series of vibrations but any 

 particular oscillation is performed at a later instant by the particle 

 which is farther away from the source of the sound. The disturbance 

 in the air which represents a spoken sound may then be pictured 



-2; 2 5 



-3.25 



0.2 0.4 



0.6 0.8 1.0 1.2 



TIME IN SECONDS 



Fig. 1 — Melodic curves showing the variation of pitch with time as the sentence 

 "Joe took Father's shoe bench out " is spoken and sung. 



either, as was first described, in terms of the successive positions of a 

 single particle or in terms of the displacements at any instant of each 

 of the particles along the line of travel of the sound wave. For 

 example, for the sentence "Joe took Father's shoe bench out," the dis- 

 turbance carrying the sound j in the word "Joe" is about fifteen 

 hundred feet from the mouth by the time the sentence is finished. 

 I have a record here which was taken in our laboratories which shows 

 the intricate motion of each particle of air as this sentence is trans- 

 mitted through the air. 



If we analyze the wave when the sentence "Joe took Father's shoe 

 bench out" is spoken, the variations in pitch of the speech sounds 

 can be determined from the vibration rate. Such an analysis is 

 shown in Fig. 1. The variations in pitch are represented on the 



