WHY IS THE HUMAN EAR IMMOBILE? 231 



behind.* It can thus be seen that in accuracy of localization the ear 

 can not be compared with the eye. The loss of the reflex apparatus 

 by which the ear turned so as to catch most readily the vibrations in 

 the air, has brought it about that the positions of sound are now so 

 imperfectly apprehended by us. 



The loss of this power of localization means two disadvantages. 

 The first may be indicated in the words of Darwin :f "The power of 

 erecting and directing the shell of the ears to the various points of 

 the compass is no doubt of the highest service to many animals, as 

 they thus perceive the direction of danger." 



Closely connected with this practical disadvantage is another. The 

 space of the ear has not the geometrical character of the spaces of 

 sight and touch. Yet there is surely no good reason for doubting 

 that it might have had much more of this character. Were the ear 

 as mobile as the eye or the fingers, it would resemble them in the 

 orderliness and well-defined character of the spatial forms it would 

 yield. That its spatial form would equal in these respects that of the 

 eye, it would be too much to affirm dogmatically. There may be more 

 conditions to supply than merely that of mobility. Yet the touches 

 from the less mobile parts of the body are singularly vague in their 

 spatial outline as compared with those from the fingers and the tongue. 

 And were the ear to gain mobility, we might expect to find it at least 

 approximating, in its appreciation of form, to the senses which are 

 regarded as so preeminently geometrical. 



It is now apparent how serious are the disadvantages involved 

 in the ear's immobility. Darwin thinks that the loss of the ear's 

 movements is partly compensated by the increased ability to move 

 the head about. It is true, these movements of the head are of im- 

 portance both in seeing and in hearing. Yet in speaking of them 

 as making up for the mobility of the sense-organs, we should be care- 

 ful not to exaggerate their value. A man whose legs have been smit- 

 ten with paralysis must find only small compensation for his affliction 

 in the fact that a strong though somewhat slow porter is, when not 

 otherwise occupied, ready to carry him about. It is also to be noticed 

 that the eye has at its disposal the head movements, yet has retained 

 its mobility. 



We have now to ask what the mental gain is which has resulted 

 from this loss. It is to be found in the ability to attend to a succes- 

 sion of sounds. 



Let us notice how distinct is our perception of succession. A sound 

 comes suddenly and sharply, and then it is gone, and another sound 



* On the localization of sound, see ' Studies in Space Perception,' by 

 A. H. Pierce. 



t ' Descent of Man,' p. 14. 



