96 
ON HEARING WITH TWO EARS. 
that nearest the source of sound with very different intensities. 
He is disposed, from some careful experiments made on an open 
lawn with different kinds of sounds, to attribute the perception of 
the direction of sounds to this inequality produced by diffraction, 
the brain drawing from the slight differences of the tones 
received in the two ears an unconscious judgment based on 
empirical observation. It is undoubtedly a remarkable fact that 
while the ears can distinguish perfectly well whether the simple 
tone of a small tuning-fork comes from the right or from the 
left, they often cannot tell one whether such a sound is immedi- 
ately in front or immediately behind. Now it is for simple 
tones that Steinhauser’s theory ought to be true if for any ; and 
it is precisely for these that it fails when put into practice in the 
Pseudophone. When the effects of diffraction are such as to be 
relatively negligible, as for shrill sounds, whose wave length is 
very small, then Steinhauser’s theory of the relative intensities 
appears to hold good. It may possibly hold good in the case of 
very low tones, where the differences of phase could be (since 
the waves are so long) only very slight. Any one may easily 
convince himself, however, that it is possible for diffraction to 
produce a very marked difference in the relative intensities with 
which the partial tones of a compound sound reach the ears. 
For this, the simple experiment suffices of comparing the note of 
a musically-ticking clock, placed in front of the head, with its 
note when placed an equal distance behind. The sound will 
seem almost as loud, but there is a very decided difference in the 
timbre of the note. 
In conclusion, it appears, in the present state of our know- 
ledge, impossible, as yet, to decide whether difference in phase, 
or in intensity, or in quality, of the sounds that reach our two 
ears is to be regarded as the criterion by which we judge of the 
direction of a sound. 
