of the Position of Sonorous Bodies. 644 
brought inte contact with two plugs of wet 
paper that closed my ears; in consequence of 
which I made the following conclusive remarks. 
When both points pressed with equal forces on’ 
the plugs of paper, I judged the watch to be 
directly before me from its beating: but as often 
as the pressure of one of the points was aug- 
mented, the sound seemed to quit its station in 
front of me, and to incline towards that side 
where the greater force was applied; lastly, I 
discovered, by using only one branch of the fork, 
that an increase of the pressure increased the 
effect of the same sound. The two cases of 
horizontal hearing being by this time pretty 
fully considered, it is necessary to change the 
subject, that the method whereby we judge. of 
elevation by the ear may be examined in its turn. 
For this purpose, suppose a right line to join 
the sonorous object, and the centre of the axis 
of hearing; also conceive a plane to pass through 
the same centre, to which the same right line is 
perpendicular. ‘Then it is evident that all the 
pulses, which are impressed by the sonorous 
object on the head, must fall on that part of it 
which lies between the plane and the place of 
the sound; consequently that portion of the head 
is the seat of the sensation excited by the sonorous 
object; because the head is a sensitive solid, and 
capable of topical irritation arising from the ime 
