[millek] photographs OF FOG SIGNALS 169 



When the trumpet is attached the sound received at the lateral 

 station is reduced to 51 per cent of that received when the trumpet is 

 removed, notwithstanding that the energy output of the diaphone is 

 probably increased by the trumpet. This conclusion is in general 

 agreement with that obtained from the observations at the wharf. 



The acoustic energy emitted by the diaphone increases with the 

 operating pressure of the air. As measured at this station, the trumpet 

 being in place, if the total energy of all frequencies is represented by 

 100 when the air pressure operating the diaphone is 18-7 lbs. per 

 square inch, then when the pressure is 23-5 lbs. per square inch the 

 energy is 230, and for a pressure of 28-8 lbs. per square inch it is 320. 

 If account is taken of the energy contained in the first five partial 

 tones only, of frequencies from 174 to 870, the partials which carry 

 the farthest, then the energy increases with the pressures mentioned 

 in the ratios of 100:300:500. The increasing air pressure increases 

 the energy of the lower partials more rapidly than of the higher ones. 



