THE EAR AND HEARING. 
345 
versa. We thus see how inferential processes control our 
judgment of distance. If we are led to imagine a sound is 
farther off than it really is we seem to hear it stronger than 
it is. Awaking suddenly in the night we hear a faint noise 
and suppose it much louder, through our temporary confused 
notion of its real distance. Hence the slight creak of a part 
of the bed or bed room furniture, the gnawing of a mouse or 
beetle, &c., originates in timid and imaginative subjects ideas 
of ghostly and burglarious sounds. 
It being an effect of distance that sounds fade away into 
a feeble hum, when we encounter a sound whose natural 
quality is feeble, like the hum of a bee, we readily imagine it 
more distant than it really is. Hence also the possibility of 
ventriloquism. The ventriloquist modifies Ins voice to 
imitate sounds proceeding from varying distances and places, 
and also tends to impose upon our judgment, through the 
effects of imagination, by directing his voice to various points, 
pretending himself to hear the sounds proceeding from 
thence. Must we then implicitly “ believe our own eyes and 
ears ” ? 
Our estimation of direction , according to our present 
knowledge, appears to be owing to a process of reasoning 
applied to the sensation. Thus we hear distinctly a sound 
emanating from a given point, whatever position the head is 
in ; but, the ear being able to judge of slight differences in 
the intensity of sounds, we remark that in certain positions 
of the head the sound seems strongest. We are hence led 
to place our head in one fixed position as regards the 
sounding body—that is, the one which shall bring the 
external meatus as nearly as possible in a straight line 
with the sounding body. Our sight tells us what is this 
direction of most perfect hearing, and we then apply the 
observation made upon bodies that we can see to those that 
are not seen. The combined action of the tiro ears 
also favours very materially the perception of direction 
of sound—as our two eyes do visual perceptions. A person 
deaf in one ear is usually unable to say whether a sound 
proceeds from before or behind. According to Weber, in 
determining the direction of sounds we employ the external 
ear for those coming from above, below, behind, before; and 
the tympanum for those coming from left to right. He 
inserted the head in water, the air passages being filled with 
air so that the tympanum was free to vibrate, and found that 
in that case the ear recognised sounds as external, but 
could only distinguish them as proceeding from the right or 
left. When, farther, the ear itself was filled with water, and 
