[king] fog signal researches 111 



Section 2. Summary of 1917 Father Point Tests. 



A series of tests was carried out at Father Point in September 

 and October, 1917, under a grant from the Advisory Council for Scien- 

 tific and Industrial Research. The following results were obtained: 



(i). Preliminary experiments were carried out on the develop- 

 ment of a rotary valve by means of which the pressure-amplitude in 

 the very intense sound-waves in and near the trumpet could be 

 measured by means of an ordinary manometer. 



(ii). A thorough investigation was made of the thermal method 

 of measuring the acoustic output of a small two-inch diaphone capable 

 of sounding a continuous blast. Temperature differences were 

 measured by means of thermoj unctions inserted one on the high 

 pressure side of the piston, the other on the low pressure side. Almost 

 continuous temperature readings were recorded as the air-pressure 

 was allowed to fall gradually from 29 to 6 pounds per square inch. 

 Although the acoustic output varied from the neighbourhood of 100 

 watts at the lower pressure to about 350 at the higher pressure, the 

 acoustic efficiency decreased from about 24 per cent at low pressures 

 to 8 per cent at the high pressures. Several series of observations 

 with and without the trumpet confirmed these results which, taken 

 with the 1913 tests on the large diaphone, indicate that higher effici- 

 ency in fog-signal apparatus may be looked for by the utilization of 

 low pressures and the separation of sources into a number of small 

 synchronized units. 



(Hi). An important problem solved during the 1917 tests was 

 the determination of the quality of the sound given out by the diaphone, 

 easily recognized by ear to be extremely complex at close quarters, 

 although fairly pure at great distances. The accurate analysis of 

 complex tones has only recently been achieved through the work of 

 Professor Dayton C. Miller of the Case School of Applied Science. 

 By means of an instrument of his invention called the "phonodeik," 

 it is possible to actually "photograph" the sound-waves in the form 

 of a sinuous line on a photographic film. The analysis of such a 

 record gives exact data as to the relative proportions of acoustic energy 

 contained in the fundamental and overtones. On receiving an invita- 

 tion from the writer to undertake a study of the quality of sound gen- 

 erated by the diaphone, Professor Miller brought to Father Point his 

 phonodeik by means of which a successful series of films was finally 

 obtained at various distances to nearly three miles. These records 

 brought out a number of interesting and important facts. It was 

 found that the sound from a small two-inch diaphone unprovided with 

 a trumpet was extremely complex. It was inferred that the effect of a 



