A SELECTIVE HOT-WIRE MICROPHONE. 
413 
except in the case of the first two deflections, when the maximum variation was 
0 *5 cm. 
Distance in 
feet. 
Deflection in 
centimetres. 
Distance in 
feet. 
Deflection in 
centimetres. 
12 
13-0 
36 
1-7 
16 
9-1 
40 
1-4 
20 
5-7 
44 
1-1 
24 
3-3 
48 
0-85 
28 
3-0 
56 
0-8 
32 
2-3 
64 
0-6 
In fig. 11 the deflection d is plotted against the distance r. By plotting log d against 
log r we obtain a straight line represented by 
logio d = 3'34-2 log 10 r, 
1 
which shows that the deflection d is proportional to —, that is, to the intensity of the 
7 ' 
sound. 
o 
10 20 30 40 50 60 70 
r in feet 
Fig. 11. 
According to the equations given in § 6, we should have 
.SB,! = — 0'23U 2 (1 — 0'0072U 2 ) 
for all values of U up to about 4 cms. per second. 
VOL. CCXXI.——A, 3 L 
It becomes of interest to estimate 
