642 On the Method of judging by the Ear 
pulses of sounds. Seeing now we are convinced, 
by a delicate sort of touch, what part of the head 
is affected by the strokes of the sonorous object, 
and are at the same time well acquainted with 
‘the form of this member of the human body, we 
judge accurately what is the situation of the 
excited portion of it, relative to the centre of 
the axis of hearing: in consequence of this judg- 
ment, we also determine the position of the plane 
last mentioned, which forms the base of the por- 
tion under consideration, by dividing it from the 
rest of the head, 
But the right line which joins the middle point 
of the axis of hearing and the sonorous body, 
points out the direction of the sound, which line 
is perpendicular to the given plane in a given 
point; for which reason it is given in position : 
or, in other words, the direction of the sound in 
respect of fixed points in the hearer’s head is 
determined: and this is done with a degree of 
accuracy, which I believe very few people are 
aware of. In order to satisfy my own curiosity. 
on the subject, I tried an experiment, with a view 
to discover what is the least sensible variation of 
a given sound from the. perpendicular to the axis 
of hearing, supposing the deviation to be measured 
by an arc of the horizon; and I found the angle 
comprehended by this perpendicular, and: the 
sound’s path, did not exceed ejght degrees, 
