v THE SENSE OF HEAEING 257 



1-12 seconds of continuous impression. Persons who are partially 

 deaf, or have disease of the middle ear, only perceive it much 

 later. Many people can only hear a strongly vibrating tuning- 

 fork or the ticking of a clock after 5, 8, or 10 seconds. Sometimes 

 one ear hears before the other, so that in binaural hearing there 

 is a kind of echo or sensation of a double sound. The eminent 

 otologist Dennert (1899) showed the importance of these observa- 

 tions in testing audition. He used a vibrating tuning-fork which 

 was rhythmically brought near or moved away from the ear of 

 the patient, and proved that the less the aural acuteness and 

 the feebler the tone, so much the greater must be the number 

 of impulses which must summate in order to obtain complete 

 perception. 



The rising or waxing phase of auditory sensation (Anklingen) 

 has its parallel in the falling or waning phase (Abldingen), which 

 is due to the fact that the sensation continues for a certain time 

 after the cessation of the physical vibration that produces it. 

 Helmholtz took as the measure of this persistence of sensation 

 the maximum rate at which two notes can be alternated in a 

 trill, without fusion of the two consecutive sensations into one 

 single sensation, as occurs with colours. The duration of the 

 falling phase in hearing varies according to Meyer, Exner, and 

 Mach with the pitch of the notes : 



For low notes (c 1 ) =0-0395-0-0209 seconds. 

 high notes (c 4 ) = 0-055 - 0-0008 seconds. 

 noises =0-016 -0-002 seconds. 



The persistence of the sensation on the cessation of the objective 

 sound may be considered as an effect of imperfect damping of the 

 vibrating parts of the ear, but it more probably depends on the 

 persistence of the central nervous excitation, as has been demon- 

 strated for other modalities of sensation. 



Methods of investigating the Function of Audition. Various methods are 

 employed by otologists in investigating the hearing of patients. Whispering 

 or in cases of more severe affection loin I speaking is generally employed. 

 The first ten numbers are usually pronounced at varying distances, and the 

 patient repeats these if able to hear them. 18 metres is generally assumed 

 to be the greatest distance at which a normal car can still hear whispered 

 words ; but according to Malte a young man with normal hearing is able to 

 hear them al :>.->- 1" metres. 



It must, however, be remembered that in using loud speaking or 

 whispering as a test of auditory acuity the select inn of the ^mnd or word 

 pronounced at a certain distance is not unimportant The auditory distance 

 varies within comparatively wide limits according to the sounds employed 

 for testing, or more exactly the vowel on which the word-accent falls. As 

 we have already seen (Vol. III. Chap. III.) single vowels, whether spoken or 

 whispered, arc pronounced with a pro^iv.-H \ civ ri.Miig cadence (tone) in the 

 series u (oo), 6 (or), o (ol), a (ah), e (a), e (e), i (ee). It is therefore easy to 

 draw up a table of two-syllable word-' embracing a series of sounds in which 

 the accented vowel varies, as follows : 



VOL. IV S 



