ATMOSPHERE AND THE ACOUSTIC EFFICIENCY OF FOG-SIGNAL MACHINERY. 257 
station in the 1-minute interval between the blasts. As a rule each of the two 3-second blasts was 
measured and the mean of the two readings entered. In some cases the readings were repeated for 
successive blasts. When more than one signal was measured the suffix indicates the number of readings 
of which the result entered is the mean. 
Chart 1. Short range acoustic survey, September 2, 1913. The more important features of the chart referred 
to in the text are : D, position of the diaphone trumpet; L, Father Point lighthouse; S, control 
station near engineer’s residence; M, meteorological station; W, control station at end of wharf. 
The pressure amplitude in the sound-waves was found to be so great within a radius of 100 feet that 
the phonometer readings were thrown completely off the scale. The readings could be brought on the 
scale by untuning the resonator. It was found, however, that the resonance curves obtained by plotting 
phonometer readings against resonator positions (as in fig. (ii.), Appendix I.) did not have proportional 
ordinates. As the intensity increased, the curves became relatively flatter. A phonometer reading taken 
with the resonator at any position other than 8 cm., could be expressed in terms of the reading which 
would be obtained at resonance by a rough interpolation from the series of resonance curves. Such 
readings, when entered in Table 1, are enclosed in brackets, and are in defect of the true resonance 
reading if it could have been obtained. As already mentioned under Appendix L, the conversion of the 
phonometer readings to pressure amplitudes by making use of the constant determined for moderately 
loud sounds is subject to some uncertainty owing to the existence of eddies in the resonator. Values 
thus obtained will, however, be in defect of the true pressure amplitude. 
The phonometer readings are shown graphically in Chart 1. It will be noticed that although the 
weather was comparatively calm, atmospheric conditions varied so rapidly that the inward and outward 
readings taken along each line at intervals of a few minutes are only in rough agreement. There is 
