320 
Mr. T. J. Bowlker on the Factors serving 
Some o£ the results obtained are given in the table below. 
In order to avoid psychological errors of imagination and 
expectation, no guesses at what would happen were made, nor 
any theory formed as to the probable position of the image 
until two or three complete sets of experiments had been 
made. It was found, however, that after a little practice the 
location of the image could usually be obtained with such 
certainty that these precautions were unnecessary. 
In the following tables r. indicates that the tube was over 
the right ear or that the movement of the sound-image was 
to the right, whilst I. indicates the same for the left. 
L is the length from the extremity of one tube to the 
extremity of the other when both are applied to the head. 
6 is the angular displacement of the image when the longer 
tube is nearer the source. 
B' is the angular displacement when the shorter tube is 
nearer the source. 
Note of Wave-length = 19 inches. 
Length of 
Diff. of 
Displacement 
L sin 9. 
Lsine'+D. 
tubes over 
length of 
of 
9 = angle to 
9' = angle to 
ears. 
ear-tubes = D. 
image=0. 
the left. 
the right. 
Inches. 
Inches. 
Inches. 
Inches. 
7 over r. | 
6 over J 
1 
2°1. 
•6 
8r. 1 
61. j 
2 
6°1. 
2-1 
9r. I 
6 1. ] 
3 
8°1. 
29 
10 r. 1 
61- 1 
4 
10° 1. 
3-7 
12 r. . 
6i. r 
6 
16° 1. 
6-7 
14 r. 1 
6 1. j 
8 
10° 1. 
4-4 
151 r. 1 
6 1. / 
H 
f 20° Land 
1 20° r. & 0° 
92 
187 
18 r. 1 
6 1. ] 
12 
f24°l. 
1 8°r. 
123 
162 
19 r. ) 
61. j 
13 
J 26° 1. 
1 6°r. 
13-6 
16-1 
Now if an image, apparently in front, is produced when 
the phases arriving at the ear are in agreement, L sin should 
be equal to the difference of length of the ear- tubes, and 
L sin 6' -f D should be approximately equal to the wave- 
length. We find that this is the case. There are, however, 
some anomalies, notably when the angle suddenly changes 
from 16° 1. with a tube 12 inches long over the right ear to 
