May 29, 1879] 



NATURE 



103 



I 



In testing the capacity of hearing, it is noticeable that 

 the power to detect the diminishing sound is maintained 

 best by continuing the reduction in trace or line while the 

 attention is fixed. A sudden break may cause the sound 

 to be lost to the listener long before his real incapacity to 

 ■hear is reached. If, for instance, the sound be very 

 faintly heard at 15°, and the induction coil be suddenly 

 moved to 5°, the sound at 5° may be quite inaudible ; but 

 if the coil be slowly moved, unit by unit, from 15° to 5°, the 

 sound at 5° niay be distinctly heard. 



The effect of filling the chest and holding the breath 

 makes a difference in listeners. The capacity for hear- 

 ing is for a few seconds mcreased by holding the breath. 

 Holding the breath with the chest not full fails to produce 

 the same result. 



As a rule, the hearing of persons who are right-handed 

 is most refined in the right ear, and as most pel sons are 

 right-handed, it is found that the right ear is the best ear. 

 This rule is, however, attended with many exceptions, 

 since, for various reasons, some persons who use the 

 right hand exclusively, practise for some particular pur- 

 pose the use of the left ear, upon which that ear becomes 

 more acute. Another point of interest attaching to this 

 observation is, that the practice of using one ear for 

 special refinement of the sense seems for the time slightly 

 to impair the other ear, although there is no physical 

 evidence of such impairment. 



Connected with the last-named fact is another, namely, 

 that by this instrument the deaf are found to fail in capa- 

 city of hearing not only by reason of physical defect, but 

 also by failure of memory of sounds. Thus in a youth 

 who had suffered serious defect of hearing for seven 

 years, owing to partial destruction of the tympanum, and 

 who in the right ear could only detect sound at 107°, there 

 was an inability to catch all the sound lying between 130° 

 and 107°, until he could remember what he had to listen 

 for. By practising him then to detect the lowest sound 

 that he was physically capable of receiving, Dr. Richard- 

 son got him to detect this one sound more readily than 

 those which came higher up. By further practice all the 

 intervening sounds became audible with equal facility. 



By use of the audiometer the influence of atmospheric 

 pressure on hearing is detectable. In Dr. Richardson's 

 own case, when the barometer is at 30° he can hear on 

 both sides close down to zero ; but below 30" he fails by 

 2° on the left side to reach zero. In another person a 

 similar failure extends to a loss of 4°. 



Dr. Richardson has tried to determine in some of the 

 lower animals whether there is the same sense of hearing 

 as in man. In two dogs, one a terrier, the other a field 

 spaniel, the range of hearing power seemed to be dis- 

 tinctly lower than it is in the human subject who has 

 perfect hearing. In both these animals, which were 

 healthy, and in the prime of life, the first indication of 

 the detection of sound commenced at 10° on the scale. 



Dr. Richardson's practical conclusions are — 



I. The audiometer will, he thinks, be an essential in all 

 physical examinations of men who are undergoing ex- 

 amination as to their fitness for special services requiring 

 perfect hearing, such as soldiers, sentries, railway offi- 

 cials, and the like. 2. The instrument will be of great 

 use to the physician in determining the value of hearing 

 in those who are deaf, and in determining the relative 

 values of the two organs of hearing. 3. In other forms 

 of diagnosis he has found the instrument useful, as in 

 anaemia and vertigo. 4. The instrument may be used to 

 differentiate between deafness through the external ear 

 and deafness from closure of the Eustachian tube — throat 

 deafness. S- The instrument promises to be very useful 

 in detecting the effects in the body of those agents which 

 quicken or excite the circulation, such as alcohol and 

 other similar chemical substances. 6. The instrument 

 promises to be of great service in determining the value 

 of artificial tympanums in instances of deafness due to 



imperfection or destruction of the natural tympanum. 

 Dr. Richardson finds in fine gold the substance for 

 making the most useful and effective artificial drum. 



The sphygmophone, for obtaining a secondary or tele- 

 phonic sound from the movements of the pulse at the 

 wrist, is devised by adding a microphone to a Pond's 

 sphygmograph. Dr. Richardson mounts on a slip of talc, 

 glass, or wood a thin plate of platinum or gas carbon. He 

 places the slip in the sphygmograph as if about to take a 

 tracing of the pulse. One terminal from a Leclanche's 

 cell is connected to the platinum or carbon, and the second 

 terminal from the cell to a terminal of the telephone, the 

 other terminal of the telephone with the metal rod of the 

 sphygmograph which supports the slip. The instrument 

 is placed on the pulse, in the ordinary way, and is adjusted, 

 with the writing needle thrown back, until a good pulsat- 

 ing movement of the needle is secured. The needle, in 

 passing over the metallic plate, causes a distinct series of 

 sounds from the telephone, which correspond with the 

 movements of the pulse. The sounds are singular, as 

 resembling the two words, " bother it." The sounds can 

 be made very loud by increasing the battery power. 



In this connection we may state that in the last number 

 of La Nature a micro-telephonic explorer is described, 

 also evidently of great use in pathology. This is a simple 

 instrument, devised by MM. Charden and Prayer, con- 

 sisting of a telephonic apparatus with microphonic inter- 

 mediary to intensify any sounds sought for, and which, 

 among other purposes, will be of great service in detecting 

 any foreign body in a vital organ. The apparatus is quite 

 portable and worked with comparative ease, though 

 doubtless actual practice will suggest improvements both 

 in this and in the applications devised by Dr. Richardson. 



A MACHINE FOR DRAWING COMPOUND 

 HARMONIC CURVES^ 



HARMONIC curves possess great importance, since 

 they represent to the eye the circumstances of 

 motion of bodies in a state of vibration, and hence apply- 

 not merely to the pendulum and to inusical instruments 

 when giving their tones, but also to the particles of air 

 during the transmission of sound. 



The study of these curves offers us two problems of 

 almost equal importance and interest, viz. : First, Given 

 the curve ; required, to find its component simple ele- 

 ments. Second, Given the component simple curves; 

 required, to construct the resulting compound curve. 

 From the standpoint of acoustics these problems may be 

 stated thus : First, Given a complex sound, required to 

 find the simple musical tones of which it is composed. 

 Second, Given the intensity, pitch, and phase of each of 

 a number of pure musical tones ; required, to find the 

 effect of their simultaneous action on the air. 



The laborious investigations of Donders, Helmholtz, 

 and others into the constitution of the simplest elements 

 of speech — the vowel sounds— show that the actual 

 analysis of the simplest articulate sound is no easy matter. 

 When the curve corresponding to the sound is once 

 obtained, Fourier's theorem enables us to subject it to 

 mathematical analysis, and thus determine by a somewhat 

 laborious process, its simple harmonic elements. Three 

 methods give us such curves. Konig* employed two 

 tuning-forks, to actually draw the curve belonging to their 

 combination ; this method is limited to combination of 

 two simple tones. Messrs. Jenkin and Ewing' magnified 

 the impression made on the tin-foil of the phonograph, 

 obtaining thus the curve belonging to the sound impressed 

 on the vibrating disk. 



■ Abstract of Paper in the American yoiimal of OUloey t<x kin\,\>J 

 Prof. E. W. Blake, Brown Universiijr 

 '' Poggeiutorff' s Annalrn, Bd. civii. S. 177, 187*. 

 3 Natuke, May 9, 1878; July 25, 1878. .■ 



