^624 



whole surface, presented a singularly mottled appearance ; and as 

 the black colour became predominant, the white portions of the 

 skin seemed like patches of irregular shape formed in the natural 

 negro skin. With the colour of the skin, that of the hair, which 

 had also become M'hite, has been gradually restored to its former 

 black hue. During this process of return to the natural colour the 

 health has been remarkably good. 



June 11, 1846. 



The MARQUIS OF NORTHAMPTON, President, in the Chair, 



"On the Physiology of the Human Voice." By John Bishop, 

 Esq., F.R.S. 



After premising a brief description of the sj^stem of organs which 

 are subservient to the voice, the author proceeds to consider the 

 several theories which have been devised to account for its various 

 modifications. These theories have, for the most part, been founded 

 on the laws which regulate the vibratory movements of stretched 

 membranous surfaces ; and the investigation of those laws has ac- 

 cordingly occupied the attention of many eminent mathemati- 

 cians, such as Euler, Bernoulli, Riccati, Biot, Poisson and Her- 

 schel; but it is a subject requiring the most profound analysis, and 

 involving the resolution of problems of much greater complexity 

 than the laws of the vibrations of either strings or bars. The as- 

 sumptions which are necessary in order to bring the subject within 

 the reach of analysis, namely, that the membrane is homogeneous 

 in its substance, and of equal thickness and elasticity throughout its 

 whole extent, are at variance with the actual conditions of the vocal 

 organs, which are composed of tissues differing in thickness, density 

 and elasticity, and of which the tension is indeterminate ; circum- 

 stances which present insuperable obstacles to the attainment of a 

 mathematical theory of their vibrations. 



The author, after giving a critical account of the experiments 

 made by Biot, Willis, Miiller, Cagniard la Tour and De Kempelin 

 on the vibrations of membranous laminae, examines the various 

 actions of the vocal organs during the production of the more sim- 

 ple tones ; and considers more especially the office of the vocal 

 ligaments, in regulating the pitch of the voice, which he considers 

 as resulting from variations in their length and tension conjointly. 

 By applying to the chordae vocales the formulae of vibrating cords, 

 he traces the influence which is exerted on their movements by the 

 mucous membranes ; and finds that they obey, to a certain extent, 

 the laws of vibrating strings. 



The analogy between the action of the glottis and that of a reed is 

 next examined, and an opinion expressed that the movements of the 

 glottis in the vocalization of the sound, partake of the nature of the 

 reed, during the partial opening and shutting of the rima-glottidis. 



