1896-97.] Dr Albert A. Gray on Direction of Sound. 
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Our Perception of the Direction of Sound. By Albert 
Alexander Gray, M.D. (Glasgow). Communicated by 
Professor M‘Kendrick. 
(Read April 5, 1897.) 
Our power of estimating the direction of sound is much less 
accurate than that of estimating the direction of light ; and, 
further, our knowledge as to the way in which this perception of 
direction occurs is much more limited in the case of sound. 
We judge with the greatest accuracy the direction of a ray of 
light, and we know that we do so almost entirely by the aid of 
the muscular sense. How do we judge the direction of a 
sound ? 
Before attempting a reply to this question it will clear that 
matter up, to a certain extent, by giving a statement of a few 
facts which have been found out by experiment, and are well 
attested by various writers : — 
(1) Individuals who are deaf of one ear have little power of 
estimating the direction of sound. 
(2) Individuals who are blind of both eyes generally show a 
power of judging the direction of sound far superior to those 
gifted with sight. This is particularly true if the eye affection 
dates from childhood. 
(3) The power of estimating the direction of sound depends 
upon its pitch and its quality. A pure tone of low pitch is very 
difficult to localise; with the higher notes this becomes easier, 
and with a compound sound it is also easy. 
(4) The accuracy with which we estimate the direction of a 
sound is greatest when the sound is in the line of axis of the 
two ears, and least when it is in the median plane of the body. 
Now, although these statements are, generally speaking, true, 
yet from some experiments which I have performed I have been 
led to believe that they must not be considered too exactly. 
The experiments were as follows: — 
The subject experimented upon was seated upon a chair and 
