146 Scientific Intelligence. 
e e 
greater or less than forty degrees, fewer rays of sound are reflected 
into the ear on that side than on the other, and the hearer imagines 
the source of sound to be situated on that side on which the sen- 
sation is more intense. Accordingly, to verify the perception, the 
~ hearer turns his head until both ears hear the sound equally loudly, 
and imagines then that he is looking in the direction of the sound, 
whereas he is looking at a point situated nearer to that side on 
which the larger effective surface exists. This observation agrees 
with Steinhauser’s theory. The illusion is very easily obtained 
by means of a loud-ticking clock, but with some persons does not 
succeed unless their eyes are blindfolded ; for when there is a 
conflict between the evidence of the eyes and the evidence of the 
ears, “pans appears to be to believe the former rather than 
the lat 
A more striking illusion occurs when the flaps of the pseudo- 
phone are reversed and adjusted so as to reflect into the ears 
stiunds which come from immediately behind the observer. In 
this case also, if a source of sound, situated anywhere behind the 
head, be observed, if the observer does not know how the fla aps are 
adjusted, he will estimate it to be somewhere in front; and, on 
turning his head about until the sounds are equally intense, he 
judges himself to be looking straight at the source of soun 
whereas it is in reality exactly in an opposite direction. This 
sound of a foataidkiig ok and with the human voice 
with shrill sounds it succeeds best, notably with the aae tick 
of a metronome, and even wi ell. 
Another experiment with the pseudophone, which gives rise 
to acoustical illusions, consists in setting one flap to catch ge 
from the front, while the other catches sakes from behind o 
above the observer. Under these circumstances the sounds seeidi 
as the observer moves his head, to come sometimes from the right, 
sometimes from the left, or sometimes from the groun 
Lastly, most of these experiments with the pseudophone can be 
repeated simply by holding the hands in front of the ears as flaps; 
but here the illusion does not always succeed, as the ebaier is 
conscious that his hands are reflecting to the ear sounds from a 
