640 On the Method of judging by the Ear 
For though the forces imparted to the two 
arcs, TCP, WDR are equal, they do not fall 
equally on the circle in respect to the points E 
and F, which represent the ears; the sound 
therefore coming from M strikes these organs 
with unequal forces, as ag be easily inferred 
from the figure. 
What I have just now demonstrated by help 
of a semicircle may be said with equal justice of 
any solid, such as the human head, that can be 
divided vertically into two equal and similar 
portions by the plane, to which the axis of hear- 
ing is perpendicular. This assertion is too evi~ 
dent to need a laboured demonstration. It was 
observed in a former part of this paper, that if 
a person stop one of his ears, and hold a watch 
near it in a close room, he will hear the sound 
of it in the direction of the open ear by reflec- 
tion, which circumstance may be sufficient to 
establish the truth of the preceding theory : but, 
in order to diversify the proof, the following 
experiment was tried. I took a wooden fork 
made of a stick of ash, which was split more 
than two-thirds of its length for the purpose ; 
the points of thé two branches turned inwards, 
and were placed at a proper distance to receive 
the head between them; a watch was then sus- 
pended upon the haft, or undivided part of the 
fork, after which the ends of the branches were 
