368 HISTORY OF ACOUSTICS. 



consider other differences of sound than those of 

 acute and grave, for instance, the articulate dif- 

 ferences, or those by which the various letters are 

 formed. Some progress has been made in reducing 

 this part of the subject to general rules ; for though 

 Kempelen's "talking machine" was only a work of 

 art, Mr. Willis's machine 19 , which exhibits the rela- 

 tion among the vowels, gives us a law such as forms 

 a step in science. We may, however, consider this 

 instrument as a phthongometer, or measure of vowel 

 quality ; and in that point of view we shall have to 

 refer to it again when we come to speak of such 

 measures. 



19 On the Vowel Sounds, and on Reed Organ-pipes. Camb. 

 Trans, iii. 237- 



NOTE TO BOOK VIII. 



(CA.) p. 347. IT appears to follow, from Mr. J. S. 

 RusselFs recent investigations respecting waves, that the 

 comparison of the motion of the air in the diffusion of 

 sound with the motion of a circular wave in water, men- 

 tioned page 340, is not exact. The latter waves are the 

 oscillating waves of the Second Order, and are gregarious. 

 The sound wave appears rather to resemble the great 

 solitary wave of translation of the First Order. See Mr. 

 Russell's Report, Brit. As. Reports for 1844, p. 361. 



