1896 - 97 .] Dr Albert A. Gray on Direction of Sound. 451 
the phase of sound-waves which reach the two membranes 
simultaneously by means of the muscular sense. 
If this view of the matter therefore be correct, it is evident 
that we will be assisted in judging of the direction of a sound by 
means of the muscular sense. And further, it is probable that 
not only may this sense give us information of the difference of 
phase in the two ears, but it may also help us in estimating 
differences of intensity in the sound as heard by the two ears, 
for it is plain that in that ear in which the sound is most intense 
the strain put upon the muscles will be greater than in the ear 
in which the sound is less loud. 
Thus, according to the explanation advanced above, the senses 
of hearing and sight have this in common, that the means by 
which we estimate direction resides in the muscular sense. 
Of course, other characteristics of sound help us in estimating 
its direction : differences of intensity and differences of quality 
with which it is heard by the two ears. The latter characteristic, 
quality, will be of especial value An enabling us to judge the 
direction of sounds with which our ear is well acquainted, and is 
thus for the most part associative. These, however, are outside 
the range of the present paper. 
Before closing I would like to point out a matter in which the 
experiments described above might be put to practical use. It 
was shown that when the chain of bones was pressed gently 
inwards, a tuning (or watch) held opposite the other ear was 
heard louder ; and it was shown, further, that this was due to a 
stimulus passing from the labyrinth of that ear. ISTow, in a con- 
dition such as fixation of the stapes in the fenestra ovalis, it is 
obvious that this reflex could not occur. The experiment might 
therefore be used for the diagnosis of such a condition. On 
a priori grounds it would appear to be a good negative test, 
but not a valuable positive one. That is to say, if a patient 
heard the sound better in the opposite ear during the inward 
pressure of the chain of ossicles, then we could safely assume 
that the stapes was not fixed. But the converse might not 
always be true, because the subject might not notice any differ- 
ence, even though the stapes were free. 
As this affection is usually difficult of diagnosis, the test 
