to determine the Direction of Sound. 
329 
observer is +90°, the point directly behind is —90° (where 
not marked negative the angle is to be taken as positive). 
Note of wave-length 13*8 in. 
Note of wave- 
length 19-2 in. 
Note of wave-length 40 in. 
Length of Angular dis- 
ear-tube. i placement. 
Length of 
ear-tube. 
Angular dis- 
placement. 
Length of 
ear-tube. 
Angular dis- 
placement. 
Inches. 
3 
-60° 
+-60 
55 
45 
36 

30 
80 
Inches. 
2 
0° 
45 
80 
75 
60 
50 
45 
36 
16 

20 
40 
60 
60 
45 
38 
20 

50 
Inches. 
4 
0° 
8 
8 
90 
90 
80 
70 
60 
60 
50 
30 
12 

5 
4 
6 
6 
5 
8 
7 . 

7 
9 
8 
10 . 
9 
8 
12 
10 
9 
14 
15 
11 
10 
12 
70 
60 
36 
11 
12i 
16 
13 
17 
14 
13 
18 
14| 

10 
15 
10 
14 
19* .... 
15 
15 
20| 
15| 
16 
17 
16" 
After this the angle of 
displacement is small. 
And it now always remains 
within 20° of 0. 
18 
19 
21 
24 
I simply record these results without attempting any ex- 
planation, beyond suggesting that sound-conduction throuoh 
the bone and some portion o£ the brain-substance may perhaps 
pkry a part in fixing the sound-zone when the image is 
perceived. 
It is to be remarked that as no special care was taken to 
suppress resonance in the above experiments, it is probable 
that some of the results are affected by it. 
In order to determine the amount o£ displacement pro- 
duced by a difference o£ phase in the arrival of sound at the 
ears, a pair of tubes 6 inches long and 2-^ inches in diameter 
were taken. A pair of flat rectangular plates 4^ inches by 
2^ inches were also taken, and in each of them a slit 
1^ inches long and ^ inch wide was cut across symme- 
trically near the centre. These plates were luted on to the 
outer ends of the ear-tubes with modelling-clay, and were so 
arranged that the central line of the slit was T 6 - of an inch 
distant from the axis of the tube. 
The observer faced the source of sound and applied these 
tubes to the ears, the slit of one tube being vertical and 
