Fog Signals. - Sound is conveyed in a very capricious way through the atmosphere. Apart from wind, large areas of silence have been found in
different directions and at different distances from the fog signal station, in some instances even when in close proximity to it. The
apparatus, moreover, for sounding the signal often requires some time before it is in readiness to act. A fog often creeps imperceptibly
towards the land, and is not observed by the people at a station until it is upon them; whereas a ship may have been for many hours in it, and
approaching the land. In such cases no signal may be made. When sound has to travel against the wind, it may be thrown upwards; in such a case
a man aloft might hear it when it is inaudible on deck. Under certain conditions of the atmosphere, when a fog signal is a combination of
high and low notes, some of the notes may be inaudible.
The mariner should not assume-
a) That because he fails to hear the sound, he is out of hearing distance.
b) That because he hears a fog signal faintly, he is at a great distance from it.
c) That because he hears it plainly, he is near it.
d) That, because he does not hear it, even when in close proximity, the fog signal has ceased sounding.
e) That the distance from and the intensity of the sound on any one occasion, are a guide to him on any future occasion.
Taken together, these facts should induce the utmost caution in closing on land in fogs. The lead is generally the only safe guide.