1879.] 



Studies in Acoustics. 



359 



music with wonderful perfection, but it fails to reproduce most of the 

 " noises " of which speech is so largely made up. The telephone is 

 also deficient in this respect, though to a much less degree. 



3. The first object of the authors was to find a disk which would 

 vibrate to the finest shades of sonorous vibrations, and which would 

 be free from those characteristic and " personal " partials which are 

 nearly inseparable from all vibrating disks, and which interfere with 

 their true action. After innumerable experiments, on almost all known 

 forms and substances, a stretched membrane of thin india-rubber 

 rendered rigid by a cone of paper, was found to give the best effects. 

 Such a disk was applied to the telephone and the phonograph with 

 fair results, and the apparatus shown in fig. 1 was then constructed to 

 record its vibrations. To the centre of the cone ab, shown in perspec- 

 tive and section in fig. 1, which was placed in a mouthpiece similar to 

 that of a phonograph, was attached an extremely fine glass tube (g), 

 which acted as a pen. The ink employed was aniline dye, and it was 

 drawn through the pen by the very slight friction exerted between its 

 point and the paper. The paper (jj) on which the curves were to be 

 drawn was the broad band frequently used for telegraphic purposes, 

 and it was moved under the pen by mechanism similar to that used in 

 the Wheatstone automatic telegraph apparatus, at a speed which could 

 be varied at will from 1 to 18 inches per second. 



4. In this way curves were obtained illustrating the sonorous 

 vibrations due to the tones of speech, but their form was not so 

 perfect as could have been wished, due to the imperfections of the 

 disk, as well as, perhaps, to the friction of the pen failing to indicate 

 the higher upper partials. Bun at a slow speed, this instrument 

 records the variations of air pressure in front of the lips ; run at a 

 high speed it records both air pressure and sonorous vibrations. It 

 thus combines the functions of Barlow's logograph and Leon Scott's 

 phonautograph. 



5. It is intended, in this paper, to confine our observations to those 

 facts illustrating vowel sounds, a graphic representation of which, 

 drawn by the new phonautograph, is given in the following sketch 

 (fig- 2). 



6. Helmholtz's theory of vowel sounds is this : — Vowels are compound 

 musical tones, or resultant sounds formed by the combination of certain 

 components or simple tones called partials. The first partial, which 

 determines the pitch of the whole, is called the prime, and the others 

 its upper partials. The partials depend upon the reinforcements due 

 to the cavity of the mouth. Vowels do not depend upon the pitch of 

 "the prime alone, or on the grouping or harmony of the partials alone, 

 but on both. The ear must distinguish each component; it must 

 recognise the kind of cavity producing the reinforcements, and there- 

 fore it determines the different vowels. This theory has been partly 



