2 3 o POPULAR SCIENCE MONTHLY. 



definite order. It is thus by virtue of the eye's movements that there 

 is secured the perception of the orderly spatial arrangement of the 

 world revealed to our vision. 



Further evidence of the important functions which the eye's move- 

 ments fulfill in perception might be adduced, but it is not desirable 

 for the purpose in hand to take up what is more complicated and 

 debatable. What has been said may suffice to call attention to the 

 great significance of the mobility of the sense organ. 



Evidence not less striking might be brought forward in regard to 

 the sense of touch; it might be shown that it is by the movement of 

 the sense organ, say, the finger tips, that explorations of the body 

 under investigation can be, in ordinary cases, best accomplished, and 

 that it is by the producing and reversing of series of touch sensations 

 that the spatial relations of tangible objects are clearly recognized. 



The ear is immobile. Accordingly it is incapable of reflex move- 

 ments for catching sounds, like those by which the eye is turned so 

 quickly to meet the light coming from an object. 



We find likewise that the perception of space by means of sound 

 is in an extremely undeveloped form. Many have gone so far as to 

 deny that sound has any spatial character. Yet surely this view can 

 not be maintained. We locate sounds to the right or left, behind or 

 in front; moreover, we distinguish sounds as differing in volume. 



Yet it can readily be seen that the spatial characters of sound do 

 not compare in precision and definiteness with those of the sensations 

 of color and touch. What is the size of the thunder? The question 

 at first seems absurd. Yet it can not be entirely absurd, for we speak 

 of the peal as heaven-filling. The appearance of absurdity is due to 

 the hopeless vagueness of the sound image in respect to extent. 



If we analyze this vagueness we find that owing to the immobility 

 of the ear we can not locate sounds with precision. All are familiar 

 with the difficulty of telling, especially in strange surroundings, whence 

 a sound comes, unless the eye gives its help. The ringing of the bell 

 of an unseen bicycle may cause us the most painful perplexity till we 

 can learn its source by sight. Psychological experiments show in de- 

 tail how untrustworthy are our attempts to localize sounds. Not that 

 they are entirely untrustworthy. It may be that sounds have a special 

 quality according to the direction from which they come and the way 

 in which they strike upon the external ear; and recognition of this 

 quality may give help towards their localization. But at the best, we 

 are not freed from manifold confusions and errors. Thus it is found 

 by experiment that while the change of position of the sounding body 

 may be soon noticed, the direction of the change may be thought to 

 be the opposite of what it is in reality. Again, relatively loud sounds 

 are located preferably in front of the head, even when their source is 



