MECHANISM OF SPEECH 451 



arbitrary and unmeaning variations in pronunciation ; but these do not 

 belong to the subject of physiology. There are, however, certain natu- 

 ral divisions of sounds as expressed by the letters of the alphabet. 



Vowels. Certain articulate sounds are called vowel, or vocal, from 

 the fact that they are produced by the vocal chords and are but slightly 

 modified as they pass out of the mouth. The true vowels, a, e, i, o, u, 

 can all be sounded alone and may be prolonged in expiration. These 

 are the sounds chiefly employed in singing. The differences in their 

 characters are produced by changes in the position of the tongue, mouth 

 and lips. The vowel-sounds are necessary to the formation of a syllable ; 

 and although they usually are modified in speech by consonants, each 

 one may of itself form a syllable or a word. In the construction of 

 syllables and words, the vowels have many different qualities, the chief 

 differences being as they are made long or short. In addition to the 

 modifications in vowel-sounds by consonants, two or three may be com- 

 bined so as to be pronounced in a single vocal effort, when they are 

 called respectively, diphthongs and triphthongs. In the proper diph- 

 thongs, as oi, in voice, the two vowels are sounded. In the improper 

 diphthongs, as ea, in heat, and in the Latin diphthongs, as <#, in Caesar, 

 one of the vowels is silent. In triphthongs, as eau, in beauty, only one 

 vowel is sounded. Y, at the beginning of words, usually is pronounced 

 as a consonant; but in other positions it is pronounced as e or i. 



An important question relates to the differences in the quality of the 

 different vowel-sounds when pronounced with equal pitch and intensity. 

 The cause of these differences was studied very closely in the latter part 

 of the last century, but it has lately been rendered clear by the re- 

 searches of Helmholtz and of Koenig. In this connection it will be 

 sufficient to indicate the results of the modern investigations very briefly. 

 It will be seen in studying the physics of sound in connection with the 

 sense of hearing, that nearly all sounds, even when produced by a single 

 vibrating body, are compound. Helmholtz, by means of his resonators, 

 has succeeded in analyzing the apparently simple sounds into different 

 component parts and has shown that the quality of such sounds may be 

 modified by reenforcing certain of the overtones, as they are called, such 

 as the third, fifth or octave. For those who are familiar with the physics 

 of sound, the explanation of the mechanism of the production of vowel- 

 sounds is readily comprehensible. The reader is referred, however, to 

 the remarks on overtones in another part of this work, under the head 

 of audition, for a more thorough exposition of this subject. The differ- 

 ent vowel-sounds may be emitted with the same pitch and intensity, but 

 the sound in each is different on account of variations in the resonant 

 cavities of the accessory vocal organs, especially the mouth. It has 



