ATMOSPHERE AND THE ACOUSTIC EFFICIENCY OF FOG-SIGNAL MACHINERY. 2.8.9 
converted into heat, a large part of which is returned to the air, passing through the piston, and therefore 
does not contribute to the temperature drop of formula (xi.). As has already been mentioned, the 
frequency does not alter very greatly with the operating pressure, while the amplitude of vibration cannot 
vary between very wide limits if the valve-system of the driving head is to produce reciprocating motion 
at all. A reference to observation 1 of Test 4, at reduced air consumption, gives for the total power 
consumed in driving the piston and emitting sound the value 0’06 H.P. We are thus justified in 
estimating that throughout the entire range of operating pressures not more than 1/10 H.P. is required to 
reciprocate the diaphone piston. To this order of accuracy the power expenditure w calculated from (xi.) 
may be attributed to external work being propagated away in the form of sound-waves. 
Test No. 1. September 13, 1913. 
No. of 
observation. 
Mean pressure 
above 
atmosphere, 
cm. mercury. 
Pressure drop in 6 seconds. 
Pressure increase Mean pressure 
in 6 seconds due drop in 6 seconds, 
to compressors. cm. mercury 
cm. mercury. {P\~p'i)- 
Resistance 
change of 
differential 
thermometers, 
sounding and 
silent. 
G-O- 
ohms. 
Sounding, 
cm. mercury. 
Silent. 
cm. mercury. 
1 
50 -8 
3 7 
3 -35 
1-0 4-5 
0 "57 
2 
60 '5 
4 2 
4-1 
0-95 5-1 
0-80 
3 
70'1 
4-5 
4 '85 
0 "9 5 -6 
0-95 
4 
79 8 
5-2 
5 - 55 
0-85 6 -2 
1 -05 
5 
89-7 
5 55 
5 *8 
0-8 i 6-5 
1 -20 
6 
99 1 
6-3 
6-9 
0-8 7-4 
1 -40 
7 
103 -0 
6 ’5 
7-1 
0 '75 j 7 ’55 
1 '40 
8 
109-0 
7 -1 
7 -35 
0'75 1 8 -0 
1 -31 
9 
118-6 
7 -5 
8 -1 
0 "75 8 "55 
1 -28 
10 
128 -2 
7 -9 
8-9 
0-75 9-15 
1 23 
11 
137 5 
9 -1 
10-15 
0-75 10-4 
1 14 
Fig. (i.). Characteristics of the diaphone. 
Results of Test 1, September 13, 1913. Air consumption normal. 
