THE EAR. 527 



perception of pitch. It is even possible to imagine that the 

 relative strength with which the two adjoining strings are 

 affected will give rise to a corresponding series of inter- 

 mediate pitches. 



THE LOCALIZATION OF SOUND. 



The ability which we possess to determine the direction 

 from which a sound comes is an acquired ability. In local- 

 izing a sound w r e instinctively move the head through a 

 series of positions and try to determine in which position 

 the sound is clearest. Having once found this position we 

 have learned by experience in which direction we must 

 then look. When the head is held perfectly immovable the 

 localization of sound is very difficult indeed; in fact, it is 

 almost impossible unless, of course, the sounds be so near 

 that the difference in the acuteness of hearing between the 

 two ears gives us a clue as to its direction. When a sound 

 is familiar we determine its distance by its strength. It is, 

 however, a purely subjective inference which it is possible 

 to vary artificially, as for instance on the stage, when by 

 soft playing, distance is suggested, while the gradual 

 strengthening of the tones is interpreted as a movement of 

 the sources of music towards the hearer. 



In the ear there are sometimes perceived sounds which 

 are not produced by regular sound vibrations. Such sounds 

 are, for instance, the buzzing of the ears produced by the 

 vibrations of air in the external meatus, when this air has 

 been separated from the external atmosphere by bits of wax 

 in the meatus, or by vibrations in the air of the middle ear, 

 caused by an unnatural closing of the Eustachian tube. 

 Beating sensations are usually caused by the pulsations of 

 the arteries in the external meatus. Sensations of friction 

 no doubt find their explanation in the circulation of the 

 blood, while the peculiar ringing of the ears which some 

 people are able to produce at will, especially when they 

 contract the muscles of mastication, is explained by some 

 as a contraction of the tensor tyinpani, and so a stretching 



