VITAL STATISTICS. 



1475 



47X years. The same terms (probable life- 

 time, equation of lite, or vie probable) are also 

 employed in speaking of persons who have 

 attained more or less advanced ages. Thus 

 the probable duration of life of a female at 25 

 years of age is about 41 years, being her actual 

 age added to the number of years required to 

 reduce the females living at that age to one 

 half. In like manner the probable duration 

 of life of a male aged 60 years is 73 years, 

 being his age added to the 13 years required 

 to reduce himself and his contemporaries to 

 one half their number. 



The term "specific intensity" has also 

 been used as a measure of the value of life. 

 It represents the number living at any given 

 are, divided by the number dying at that 

 age. For example, if, at the age of 44, 72,709 

 male survivors of the population of Eng- 

 land and Wales, out of 100,000 born into 

 the world, lose by death 990, the specific 

 intensity is if&a or 73-475, while for the 

 number of 72,190 female survivors losing 923 

 of their number, the specific intensity is 2 f , 

 or 78-/J09. Females, therefore, have a higlier 

 intensity of life at 43 years of age than males ; u 

 in other words, they suffer from a less mor- 

 tality.* 



Such are some of the principal methods 

 which have been recommended or employed 

 for ascertaining the true duration of human 

 life, a branch of statistical inquiry which 

 has received large contributions of late years, 

 many of which, however, are unfortunately 

 rendered altogether valueless by the omission 

 from the calculations of some elements ne- 

 cessary to precision, but not yet obtainable. 



BIBLIOGRAPHY. 1. The fifth and sixth annual 

 Reports of the Registrar General. 2. Contributions 

 to Vital Statistics. By F. G. P. Nelson, Esq. 3. 

 Quarterly Journal of the Statistical Society, vol. vii. 

 Essays by Edwin Chadu-ick, Esq. and F. G. P. 

 Nelson, Esq. at pp. 1. and 40. On the subject of 

 the Construction, Properties, and Applications of 

 Life Tables, which is intimately connected with 

 Vital Statistics, many interesting details and full 

 references to authorities will be found in Mr. Farr's 

 letters to the Registrar General in the fifth and 

 sixth Annual Reports. 



(W. A. Guy.) 



VOICE.f (Syn. Gr. <J>o TJ ; Lat. Vox ; Fr. 

 Voix ; Germ. Stimme ; It. Vce; Span. Toe.) 

 This term is usually applied to those sounds 

 which animals produce by means of the 

 air traversing their organs of voice, such as 

 we observe in mammalia, bird?, reptiles, and 

 in some insects. 



The human voice is susceptible of several 

 modifications, such as timbre or quality, in- 

 tensity, and pitch ; including those successive 

 transitions of tone from one pitch to another 

 which constitute melody. The organs of 

 voice comprise the thorax with the muscles 



* See Contributions to Vital Statistics. By 

 F. G. P. Neison, F. L. S. &c., p. 5. 



f [It was intended that this article should have 

 comprehended Voice and SPEKCH. It is now found 

 necessary to defer the latter subject to the Supple- 

 ment. ED.] 



of respiration, the lungs, trachea, larynx, 

 pharynx, mouth, tongue, nasal cavities, nerves, 

 and blood-vessels. Of these, the thorax and 

 lungs may be considered an air-chest or 

 bellows, the trachea a porle-vunt or air-pipe, 

 and the glottis a complex ree.l. The trachea 

 varies in length and diameter with the age 

 and sex of individuals, until they arrive at the 

 adult period of life. By its structure the 

 trachea is endowed with elasticity, together 

 with the power of longitudinal extension and 

 relaxation, and of increasing or diminishing in 

 diameter : the acoustic effect of these pro- 

 perties will presently be investigated. 



The sum of the areas of the two 

 bronchi is greater than that of the trachea ; 

 by which adaptation the latter is more readily 

 supplied with air during the vocalization of 

 the breath. in all mammalia, birds, and 

 reptiles, the axes of the bronchi are inclined 

 to that of the trachea at a greater or less 

 angle. With reference to the voice, the 

 larynx is the most important organ in the 

 whole apparatus. The mouth, fauces, tongue, 

 and nasal organs are not necessary to the 

 production of voice ; nevertheless they exer- 

 cise a considerable influence on its quality, and 

 are indispensable for the production of arti- 

 culate language. The thorax is sufficiently 

 capacious to contain as much air after a 

 full inspiration as will sustain the glottis in a 

 state of vibration, when the tone is of mo- 

 derate intensity, during the space of fifteen, 

 seconds, which will enable a person to pro- 

 nounce in rapid succession from thirty to forty 

 monosyllables at one expiration.* 



The phenomena of the voice of animals 

 must at a very early period have afforded to 

 physiologists proof of the susceptibility of 

 membranous structures to enter into a stale 

 of vibration ; and it is now generally known 

 that membranes, whether twisted into a cord 

 like the string of a violin, or in the form of a, 

 parallelogram stretched in one direction as 

 the vocal ligaments, or in that of discs 

 stretched all round as the head of a drum, 

 are all capable of producing musical sounds 

 when properly excited. 



The theory of the vibratory movements of 

 stretched membranous surfaces has occupied 

 the attention of many of the most celebrated 

 mathematicians, such as Euler, Bernoulli, 

 Kiccati, Biot, Poisson, Sir John Herschel, 

 and others. It is a subject requiring the most 

 profound analysis, and the solution of pro- 

 blems of much greater complexity than those 

 either of strings or bars ; but in order to bring 

 the theory of vibrating membranes within the 

 reach of computation, the membranes are 

 supposed to be homogeneous and of equal 

 thickness and elasticity. Now this hypo- 

 thesis will not satisfy the conditions of the 

 vibratory movements of the vocal organs, 

 such as the windpipe for example, which is 

 composed of tissues of variable thickness, 

 density, and elasticity; it would therefore be 



* For the anatomy of the human larynx, reference 

 is made to the article LAUYNX. 



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