ATMOSPHERE AND THE ACOUSTIC EFFICIENCY OF FOG-SIGNAL MACHINERY. 261 
thus bearing out the accepted theory of the refraction by an opposing wind of the sound over the observing 
ship. In spite of the comparatively high velocity of the wind, propagation at right angles to its direction 
remains fairly good (observations 15 to 35). On the inward course the wind veered to a direction opposite 
to that of sound propagation; the effect on the gradient is seen to be very marked. 
No. 6. September 4, 1913. Table 6 and Chart 6. 
The ship was kept to a circular course by navigating so as to keep the Father Point lighthouse directly 
abeam, and makmg corrections on the course by keeping the angle subtended by the top and bottom of 
the lighthouse constant. Note the diminution of intensity on entering the acoustic shadow of the Father 
Chart 6. Acoustic survey, September 4, 1913. 
Point wharf. The distribution of amplitude along the outer of the two circular courses is much greater 
than would be exjiected according to the inverse-square law of propagation, in spite of an opposing wing, 
indicating reinforcement by refraction from the upper layers of the atmosphere or by sound scattered from 
eddies. The subject is further discussed in Section (iii.) of the present Appendix. 
No. 7. September 5, 1913. Table 7 and Chart 7. 
A comparison with Chart 5 shou r s the deadening effect of an off-shore breeze. Besides containing large 
2 M 2 
