236 DR. LOUIS YESSOT KING ON THE PROPAGATION OF SOUND IN THE FREE 
discussed in detail in connection with the Father Point observations described in 
Appendix II. 
(ii.) Discussion of the Father Point Acoustic Surveys. 
By the use of the Webster phonometer it was found possible to measure from 
day to day the amplitude of the sound-waves in the neighbourhood of the Father 
Point fog-signal station, thus obtaining a permanent record of variations in conditions 
of propagation depending on meteorological conditions as far as the latter could be 
observed. In many respects this station was extremely well suited to the work in 
hand. The surrounding country for several miles is very flat and low-lying, thus 
reducing to a minimum the effect of local topography on the propagation of sound at 
sea. The existence of a permanent meteorological station at this point, together 
with good wharfage facilities, proved to be very convenient in carrying out the 
acoustic surveys. 
An inspectioii of the charts reproduced in Appendix II. indicates at once that 
wind is by far the most important factor in interfering with the propagation of 
sound. This is especially marked when the wind velocity exceeds 25 miles an hour. 
On August 25, 1913, on a course bearing N. from the fog-signal station the sound 
was lost completely at 8590 feet, the wind blowing from the west with a speed of 
about 25 miles an hour. On calmer days, with the wind in the same quarter, the 
signals will easily carry three or four times this distance. 
The more important features relating to the influence of wind and eddy-motion 
on the propagation of sound are pointed out in Appendix II. The curious undulatory 
character of many of the amplitude gradients (in particular that shown in Chart 
No. 4, August 30, 1913) may be adduced as evidence of a tolerably regular eddy- 
structure of the atmosphere. The effect of the wind on the propagation of sound 
according to the evidence detailed in Appendix II. may be summed up as follows :— 
(1) A breeze blowing in the direction of the shore line gave rise to the most 
unfavourable conditions of sound propagation (Charts 8, 9 and 10) ; somewhat less 
unfavourable is an off-shore breeze (Chart 7). These conditions may be so 
unfavourable as to counteract the propitious effect of a breeze blowing in the direction 
of sound propagation. During the daytime a shore-line breeze is the seat of 
noticeable temperature fluctuations which probably assist a very irregular eddy- 
structure in destroying the sound. An off-shore breeze may owe its destructive 
character in part to an eddy-formation accentuated by the irregular character of the 
land (trees, buildings, &e.), and, to a greater extent, in the writer’s opinion, to the 
turbulent character of the atmosphere on the leeward side of the fog-alarm building, 
in the immediate vicinity of the diaphone trumpet. 
(2) A breeze blowing shorewards gives rise to comparatively favourable 
conditions of sound propagation (Charts 5 and ll). This is apparently due to the 
regular eddy-structure and temperature homogeneity of a wind which has blown over 
