268 PRACTICAL PHYSIOLOGY 



two ears, and let it be placed opposite the open ear at such a distance 

 that its ticking is just appreciable. In a quiet room this distance may 

 vary from 2*5 to about 5 meters. Repeat the experiment with the other 

 ear. 



2. Auditory Fatigue. The full effect of any sudden sound tends to 

 temporary fatigue, to abolish appreciation of the fainter echoes which 

 succeed it. If the full effect be avoided the fainter echoes may be 

 heard. 



EXPERIMENT I. Let a sudden intense sound (such as may be made 

 by striking a bench with a hammer) be produced, (a) with the ears 

 open, (b) with the ears closed for about half a second after the impact. 

 In the first case the intense sound will alone be noticed, in the second 

 case fainter echoes will be noticed in opening the ears. 



EXPERIMENT II. Strike a tuning fork and place it on the crown of 

 the head with gentle pressure. When the sound is no longer heard, 

 remove it for a few seconds and then replace it again when the sound 

 will be again appreciated. 



EXPERIMENT III. Using a binaural stethoscope, sound a tuning-fork 

 on a stand, and standing symmetrically with respect to the fork let the 

 opening of the stethoscope be directed towards the fork. Then pinch 

 one tube of the stethoscope, and the sound will be located by means of 

 the patent tube only. When the sound has almost died away reopen 

 the pinched tube, and now the sound will appear differently located and 

 more intense to the ear which has not been fatigued. 



3. Appreciation of Pitch. EXPERIMENT. With Galton's whistle 

 or some apparatus which will provide variation in pitch, observe 

 the highest pitch in which tone can still be recognised. Conversely, 

 note the lowest audible pitch in which tone can still be heard. 



4. Recognition of Absolute Pitch. By practice a trained musician 

 can name the pitch of different tones. Education is required more for 

 this probably than in naming fine differences of colour. 



EXPERIMENT. Sit with the back to a piano and name the notes 

 struck at random by the observers. In many cases this experiment 

 may be impracticable. 



5. Beats. If two tones of different pitches be produced at the same 

 time they mutually interfere and the resultant sensation is marked by 

 a rhythmic variation in intensity, and is described as characterised by 

 beats. 



EXPERIMENT I. Put two tuning-forks of different pitches into 

 vibration, and frequently the rhythmic beating is easily recognised. 



