Transactions of the Royal Society of Canada 



SECTION III 



Series III DECEMBER, 1918, and MARCH, 1919 Vol. XII 



Summary of Fog-Signal Researches carried out at Father Point, Que., 



1913 and 1917. 



By Louis Vessot King, M.A.,D.Sc., Associate Professor of 

 Physics, McGill University, Montreal. 



(Read May Meeting, 1918) 



Section 1. Summary of 1913 Father Point Tests 



It has long been known that steam and compressed-air sirens 

 employed as fog-signals on land stations and on ships are extremely 

 inefficient when the ratio of power input to acoustic energy emitted 

 during a blast is considered. In the case of steam-whistles and sirens 

 on board ships the inefficiency is further aggravated by the large waste 

 of live steam involved. 



In the autumn of 1913 the writer undertook a series of tests on 

 the fog-signal situated at Father Point, Que. The particular type of 

 siren tested is known as the "Northey diaphone" and was operated by 

 compressed air. A special thermodynamic method was devised by 

 the writer to obtain a rough measure of the proportion of energy 

 (available as potential energy of compressed air) converted into aerial 

 sound-waves. Measurements of the rate of falling off of the intensity 

 of the sound were carried out to distances of 8 miles, making use for 

 the purpose of a sound-measuring instrument known as the Webster 

 phonometer, enabling the compression in the sound-waves to be meas- 

 ured in absolute units. The main results obtained from this series 

 of tests may be enumerated as follows: 



(i). The acoustic efficiency of the diaphone measured at the 

 constricted portion of the conical trumpet is in the neighborhood of 

 5 per cent at normal operating pressure of about 25 pounds per square 

 inch. 



(ii). The compression in an aerial sound-wave corresponding 

 to the transmission of the observed amount of energy as sound over 

 the cross-section of the narrowest part of the conical trumpet of the 

 diaphone is as high as ± 0-1 atmosphere. A theoretical investiga- 



Sec. Ill, Sig. 9 



