112 THE ROYAL SOCIETY OF CANADA 



trumpet of correct design is to concentrate the greater proportion of 

 power in the master tone. From an inspection of the photographs it is 

 clearly shown that the high overtones do not travel far but are filtered 

 out by the action of the eddies. The master tone alone survives to an 

 appreciable extent at distances greater than two miles. It is obvious 

 that the overtones produced by a diaphone or siren represent waste of 

 power and that the object of a designer of such apparatus is to con- 

 centrate the greatest possible amount of energy into the master tone. 

 (iv). Mention has already been made of the fact that of all 

 atmospheric conditions, the velocity and eddy structure of the wind 

 are by far the most important conditions affecting the propagation of 

 sound. In the present sejries of tests provision for more comprehensive 

 meteorological observations were made. While acoustic surveys 

 were carried out at sea by means of the Webster phonometer (which 

 measures the master tone of frequency about 180) with the assistance 

 of Lieutenant E. S. Bieler, observations of wind velocity at altitudes 

 of several thousand feet were carried out by sending up small pilot 

 balloons and following their motion by specially designed theodolites. 

 This part of the work was in charge of Mr. John Patterson and Dr. 

 A. N. Shaw; as a result of their investigations, the technique of meteoro- 

 logical observing to be carried out in connection with fog-signal 

 tests has been fully worked out. Anemometers of various types were 

 tested and compared, while a simple form of pitot-tube for observing 

 the gustiness of the atmosphere was designed and found to be ex- 

 tremely serviceable. It is hoped on future occasions to obtain a large 

 number of acoustic surveys under a great variety of atmospheric 

 conditions. A graphical representation of sound intensity combined 

 with one of upper air wind structure may be expected to give informa- 

 tion of value to fog-signal engineers. 



Section 3. Note on Future Problems in Acoustic 

 Engineering 



The researches just described may be considered to have estab- 

 lished the possibility of employing methods of physical measurement 

 in the field of acoustic engineering. The Webster phonometer has 

 been shown to be well adapted to the selective measurement of the 

 master tone and to carrying out acoustic surveys by means of which 

 the effect of atmospheric conditions on the propagations of sound may 

 be graphically recorded. For a study of the quality of sound emitted 

 the "phonodeik" devised by Professor Miller has been proved capable 

 of use under open-air conditions. For the measurement of acoustic 

 output and efficiency the thermal method devised by the writer seems 



