of Edinburgh, Session 1873-74. 
255 
5. Preliminary Note on the sense of Rotation and the 
Function of the Semicircular Canals of the Internal Ear. 
By Professor A. Crum-Brown. 
As far as I am aware, the sense of rotation has not hitherto 
been recognised either by physiologists or by psychologists as a 
distinct sense, but a little consideration and a few experiments 
seem to me to be enough to show that it really is so. By means 
of this sense we are able to determine' — a , the axis about which 
rotation of the head takes place ; b, the direction of the rotation ; 
and c, its rate. 
In ordinary circumstances we do not wholly depend upon this 
sense for such information. Sight, hearing, touch, and the mus- 
cular sense assist us in determining the direction and amount 
of our motions of rotation, as well as of those of translation ; but 
if we purposely deprive ourselves of such aids we find that we 
can still determine with considerable accuracy the axis, the direc- 
tion, and the rate of rotation. The experiments that I have made 
with the view of determining this point were conducted as follows : 
a stool was placed on the centre of a table capable of rotating 
smoothly about a vertical axis ; upon this the experimenter sat, his 
eyes being closed and bandaged; an assistant then turned the 
table as smoothly as possible through an angle of the sense and 
extent of which the experimenter had not been informed. It 
was found that, with moderate speed, and when not more than 
two or three complete turns were made at once, the experimenter 
could form a tolerably accurate judgment of the angle through 
which he had been turned. By placing the head in various posi- 
tions, it was possible to make the vertical axis coincide with any 
straight line in the head. It was found that the accuracy of the 
sense was not the same for each position of the axis in the head, 
and further, that the minimum perceptible angular rate of rotation 
varied also with the position of the axis. 
The sense of rotation is, like other senses, subject to illusions, 
rotation being perceived where none takes place. Vertigo or 
giddiness is a phenomenon of this kind. 
When, in the experiments just mentioned, rotation at a uniform 
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