to determine the Direction of Sound. 
321 
10°1. when the tube is made 14 inches long. This is doubt- 
less due to resonance in the 14-inch tube increasing the 
intensity at the right ear. Subsequent experiments confirmed 
this view. In later experiments large loose wads of cotton- 
wool were inserted at the outer ends of the tubes. This 
proves a very effective means of checking resonance, whilst 
not interfering very much with the intensity. In this manner, 
using sounds of various wave-lengths, it was proved that 
an image appeared in front of the observer when the 
phases of the waves arriving at the ears were approximately 
in agreement. A better arrangement was devised, however, 
later, and an account of these later experiments appears 
further on. 
The next point was to determine, to what extent the image 
of the source was displaced whilst the observer continually 
faced the source, and how this displacement depended on the 
wave-length. For this purpose two tubes were taken, and 
the observer continually faced the source and tried to note 
the direction in which the image appeared : in some cases 
only one tube was applied to the ear. 
One example is given below. 
Xote of ^Wave-length 26*8 inches. 
; Length of 
tube placed 
over one 
ear — the 
Angular dis- 
placement of 
sound- imaee 
with tube over 
Angular dis- 
placement of 
sound-image 
with tube over 
Lengths of 
tubes placed 
over the 
Angular dis- 
placement 
with the 
longer tube 
Angular 
displace- 
ment with 
the longer 
other ear 
free. 
the right ear. 
the left ear. 
two ears. 
over the 
right ear. 
tube over 
the left ear. 
Inches 
Inches. 
4 
4= 1. 
2°r. 
9 &6 
16=1. 
4 3 r. 
6 
8°1. 
4= r. 
12 & 6 
26 D 1. 
8°r. 
8 
20° 1. 
10° r. 
9 
24° 1. 
16= r. 
15 &6 
40° 1. 
14° r. 
12 
36°]. 
24 c r. 
17 & 6 
60° 1. & 60= r. 
20° r. 
15 
40°l.&40=r. 
30° r. &30=1. 
19 &6 
30° r. 
45° r. 
17 
40 c r. 
40= r. & 40° 1. 
23| & 6 
12° r. 
30° r. 
18 
19 
20 
30° r. 
20° r. 
10° r. 
30= 1. 
24° 1. 
16° 1. 
25 &6 
-•{ 
(?)0°r. & 
(?) 0° 1. 
21 
= 
8°1. 
22 
0° 
O 
28 & 6 
4=r. 
C?) 0= l. 
24 
4=1. 

28 & 4 
4°1. 

26 
10° i. 
4°r. 
27* 
20 3 1. 
8 3 r. 
It would appear from the above that the image crosses 
over from left to right, or from right to left, when there is a 
