It is in times of fog that the navigator must be given the greatest protection. As this is impossible to accomplish visually, appeal must be made to his ear. In the early days of lighthouse engineering the methods of conveying audible warning were very crude. The discharge of a gun was the most popular, but it was neither serviceable nor reliable, and was made upon somewhat haphazard lines. Thus, in the case of a dangerous headland on the North American coast, which the Boston steamer had to round on its journey, the keepers mounted guard at the probable time of the vessel’s arrival off this point. They listened eagerly for the steamer’s whistle, and when it came screaming over the water they began hurriedly firing a carronade, keeping up the blank-cartridge bombardment until another shriek told them that those on the vessel had heard their signals. Sometimes the whistle was heard from a distance of six miles; at others from not more than two miles away. It depended upon circumstances. Obviously, such a primitive system was attended with considerable danger, as an accident was liable to happen to the men in their feverish haste to load and discharge the gun, while the plight of the boat was far from being enviable at times. [Illustration: _By permission of Messrs. Chance Bros. & Co., Ltd._ A MODERN LIGHTHOUSE SIREN PLANT. Showing gas engines and air-compressors in duplicate, with siren at side.] In the early days every lighthouse tower was provided with a heavy bell. Indeed, the ponderous dome of metal projecting from the lantern gallery was considered indispensable. The bell varied in weight from 1,200 to 2,240 pounds, was fitted with a massive clapper, and when struck emitted a deep musical note. In order to enable the seafarer to gain some idea of his whereabouts, the fog-signals were given a sound-characteristic somewhat upon the lines of those in connection with the light. Thus, one lighthouse would give one stroke every ten seconds; another would give two strokes in quick succession, followed by a long silence, and so on. This system suffers from the severe handicap that the sound does not travel very far during foggy weather. Another ingenious engineer recommended the utilization of the locomotive whistle, giving a high-toned, ear-piercing shriek, but the same objection as attended the use of the bell prevailed: the sound could not be heard more than a short distance away. The British lighthouse authorities submitted the idea to a series of searching investigations to ascertain its possibilities, but eventually were compelled to conclude that it was not superior to, if as good as, the other systems then in vogue. The United States authorities, as a result of their independent experiments, expressed a similar opinion; but in Canada practical application gave this whistle a favourable verdict.