On our Perception of Sound Direction. 



215 



the experiment the ear, say the right, nearest to the falling 

 -water is stopped with the right hand. The comparatively 

 t'eehle sound then heard may be much increased if the left 

 hand be so held at a little distance out as to reflect the sound 

 into the left ear. The effect remains conspicuous even when 

 the hand is held out at fall arm's length. Of course a reflector 

 larger than the hand is still more effective. 



The discrimination between the right and left situations of 

 high sounds is thus easily explained upon the intensity theory; 

 but this theory becomes less and less adequate as the pitch 

 falls. At a frequency of 2b6 (middle c = c) the difference of 

 intensities at the two ears is far from conspicuous. At 128 

 it is barely perceptible. But although the difference of 

 intensities is so small, the discrimination of right and left is 

 as easy as before. 



There is nothing surprising in the observation that sounds 

 of low pitch are nearly as well heard with the further as with 

 the nearer ear. When the wave-length amounts to several 

 feet, it is not to be expected that the sound (originating at a 

 distance) could be limited to one side of the head. The 

 question is well illustrated by calculations relating to the 

 incidence of plane waves upon a rigid spherical obstacle, 

 and the results may conveniently be repeated here from 

 4 Theory of Sound/ § 328. 



2ttc 



M- 



F+e.G. F 2 +G'- 



l 



2 



i 



1 



-1 







•522 + -139 i 

 159- -484 i 



•430- -217 i 



•294 

 •260 

 •232 



1 



1 



-1 







•668 +-238 i 

 -•440- -303 i 

 +•322- 365 i 



•503 

 •285 

 •237 



2 



1 



-1 







■797+ -234 i 

 •250+506 8 



— •154— *577 i 



•690 

 •318 

 •356 



In this table zttc is the circumference of the sphere, and 

 X is the wave-length of the sound. The symbol jm denotes 

 the cosine of the angle at the centre of the sphere between 

 the direction of the sound (/t=l) and the point upon the 



