ATMOSPHERE AND THE ACOUSTIC EFFICIENCY OF FOG-SIGNAL MACHINERY. 269 
along line VII. The wharf was 15 feet above the level of the beach and was 37 feet broad, consisting of 
timber cribwork filled with heavy stones. 
The following readings were taken :— 
(1) 5 feet above beach and about 2 feet from nearer vertical wall.1 ■ 1 
(2) On wharf 15 feet higher on edge nearest to signal.2-4 
(3) On wharf at most distant edge.1 "2 
(4) In acoustic shadow 5 feet above beach and 2 feet from further vertical wall . . 0 ■ 2 
(5) 10 feet from foot of wharf in acoustic shadow.■ . . . 0 - 3 
(6) 20 feet from foot of wharf in acoustic shadow.l'O 
That the reading at position (2) at the higher level is considerably greater than that at position (1) 
nearer the ground may be attributed to the attenuation of the sound by the rough ground intervening 
between the wharf and the fog-signal. 
On September 19, a few observations were taken in the neighbourhood of the lighthouse (L, Chart 1), 
built of concrete in the form of an octagonal cylinder about 15 feet in diameter supported by eight flying 
buttresses (Plate (i)). Phonometer reading on nearer side of lighthouse, 9 - 0, on opposite side in acoustic 
shadow, 4 - 7. 
In taking observations from the C.G.S. “Lady Evelyn” it was noticed when manoeuvring close to the 
fog-signal that whenever the fog-signal could not be viewed directly from the phonometer, owing to the 
interposition of one of the deck structures in the line of sight, the readings were sensibly diminished, 
indicating the existence of noticeable shadows. 
In the case of obstacles of smaller dimensions (e.g., empty sheet-iron gasoline drums, about 2 feet in 
diameter) no appreciable acoustic shadows could be detected. 
Table 1. —Short Range Acoustic Survey, September 2, 1913. 
Father Point Meteorological Observations. 
Barometer, 30 '22. Air temperature : dry bulb, 56° F.; wet bulb, 53° F. 
Wind, very light breeze during forenoon. Velocity : 10-11 a.m., 2 miles per hour from E. ; 11-12 a.m., 2 miles per hour 
from E.; 12-1 p.m., 9 miles per hour from E.; 1-2 p.m., 5 miles per hour from E. ; 2-3 p.m., 2 miles per hour from W.; 
3-4 p.m., 2 miles per hour from W.; 4-5 p.m., 4 miles per hour from W. 
Weather during forenoon, clear. Few clouds visible. Sky 10 per cent, overclouded. Sky becomes overcast and wind 
veers about 2.30 p.m. 
Phonometeb Readings. 
Note . —Readings taken at positions 50 feet apart and are entered in chronological order. Position 1 is in each case 50 feet 
from the resonator of the diaphone. Unless otherwise indicated by a suffix, the entries are the mean of the two readings for 
each of the 3-second blasts. All readings, other than those enclosed in brackets ( ), were taken with resonator in position 8. 
Line II. 
Position 
No. 
Phono¬ 
meter. 
Position 
No. 
Phono¬ 
meter. 
Position 
No. 
Phono¬ 
meter. 
Position 
No. 
Phono¬ 
meter. 
Position 
No. 
Phono¬ 
meter. 
1 
11 
7'0, 
21 
2 '1 
31 
3 1 
41 
10 1 3 
2 
— 
12 
4 '7! 
22 
1 '4 
32 
2'8 fi 
42 
11 '3-, 
3 
10 '5, 
13 
4 '8, 
23 
1 '5, 
33 
3'4 3 
43 
8'lr, 
4 
9 7! 
14 
4'9! 
24 
1 1 
34 
5 '6[ 
44 
9 '2 
6 
10 '0! 
15 
4 li 
25 
1 1 
35 
4 0| 
45 
9 '7 
6 
9 '4[ 
16 
4 '6 
26 
1'2 4 
36 
4 '4, 
46 
7 '9 3 
7 
9'5, 
17 
4'9 
27 
1 '5 
37 
6 '2, 
47 
13 '8, 
8 
9 3, 
18 
4 '0, 
28 
2 '9 
38 
7'2 4 
48 
(>48) 
9 
8 '2, 
19 
3 '7 
29 
1 '9 
39 
9'2 fi 
10 
8 '0, 
20 
3 '4 
30 
1 '9 
40 
11 -o 
Eemarkt. 
Readings plotted on Charts 1 and 2. Wind, 2 miles per hour from E. Observations at control station, 10.27 a.m. : mean 
of three phonometer readings, 7 '7. 
2 n 2 
