Lightships and Lighthouses

by Frederick Arthur Ambrose Talbot

While Professor Holmes was experimenting with this device, another investigator, Mr. Slight, of Trinity House, was wrestling with the same problem. Indeed, he may be described as the inventor of the modern siren. Although he effected only an apparently slight modification, it was the touch which rendered the instrument perfect, while it also removed the possibility of a breakdown at a critical moment, as he rendered the moving part freer in its working and eliminated the severe strains to which it was subjected. The improvement was appreciated by Professor Holmes, who adopted it immediately.

While these indefatigable efforts were in progress, ingenious attempts were made to press Nature herself into operation. As is well known, there are many “blowing-holes” distributed throughout the world, where the water by erosion has produced a long, narrow cavern in the base of a rock, with a constricted outlet into the outer air. The waves, rushing into the cave, compress the air within, which, in its escape at high velocity through the small vent, produces a bellowing sound. It was this curious phenomenon which gave the Wolf Rock its name. General Hartmann Bache, of the United States Engineers, attempted in 1858 to make use of a blowing-hole on one of the Farallon Isles, lying forty miles off the entrance to San Francisco Bay. A chimney was built with bricks above the orifice, through which the air compressed by the waves below made its escape, and on top of this shaft a locomotive whistle was placed. The first effort was a dead failure, because the force of the rush of air was so great that it carried away the chimney; but in the second attempt success was achieved, and an excellent automatic whistle blared out night and day almost continuously and was audible for some distance out to sea. The only drawback was that in foggy weather, when the most intense sound was required, the signal was dumb owing to the smoothness of the water. This novel signal was maintained for some time and then was superseded by a powerful siren.

One of the most interesting fog-signalling installations in service is that on the bald formidable hump of rock lying in the estuary of the Clyde, known as Ailsa Craig. For years this rock constituted a terrible menace to the crowded shipping of this important marine thoroughfare, and its victims were numerous. While the Commissioners of Northern Lighthouses mitigated its terrors as far as possible by the provision of a powerful light, they recognized the fact that a visual warning did not meet the situation completely. But the installation of a fog-signal was a somewhat peculiar problem, owing to the configuration of the rock. A single station would not meet requirements, because it was necessary to throw the warning from both sides of the obstruction. The provision of two sound-stations would have been an expensive matter, even if it had been feasible, which it was not, owing to the precipitous nature of the cliffs.

An ingenious solution was advanced by Mr. Charles Ingrey, C.E. He proposed to erect a central power-station and to control the sounding of two sirens, placed on opposite sides of the island, therefrom, the compressed air being led through underground piping. The plans were submitted to Messrs. Stevenson, the engineers to the Northern Lighthouse Board, who, after examining the proposal thoroughly, gave it their approval. But when it came to obtaining the sanction for the requisite expenditure from the Board of Trade, that august body, despite the fact that the project had been investigated and had received the approbation of the engineers to the Northern Lighthouse Commissioners, declined to permit public money to be expended upon an untried scheme. Such is the way in which pioneering effort and ingenuity are stifled by Government departments.

THE ACETYLENE FOG-GUN.

The latest ingenious device for giving both audible and visual warning automatically.

Many another engineer would have abandoned the project after such a rebuff, but Mr. Ingrey without any delay laid down a complete installation upon the lines he contemplated on the island of Pladda, where a Holmes fog-horn was in service. With the aid of a workman whom he took from Glasgow, the light-keepers and some farm labourers, this trial installation was completed, the piping being carried round the island from the air-compressing plant to the fog-signal. The work occupied about a fortnight, and then, everything being ready to convince the sceptical Board of Trade, the inspecting engineers were treated to a comprehensive and conclusive demonstration. They were satisfied with what they saw, appreciated the reliability of the idea and gave the requisite sanction. Forthwith the Ailsa Craig Island installation was put in hand and duly completed.

This plant possesses many ingenious features. As the light is derived from gas distilled from crude oil, a small gas-making plant is installed on the island, and this is used also for driving a battery of five eight-horse-power gas-engines—four are used at a time, the fifth being in reserve—to supply the thirty-horse-power demanded to operate the fog-signal. The energy thus developed drives two sets of powerful air-compressors, the four cylinders of which have a bore of 10 inches by a stroke of 20 inches, the air being compressed to 80 pounds per square inch and stored in two large air-receivers which hold 194 cubic feet. From this reservoir pipes buried in a trench excavated from the solid rock extend to the two trumpets, placed on the north and south sides of the island respectively. The length of piping on the north side is 3,400 feet, and on the south side 2,500 feet. At places where the pipe makes a dip, owing to the configuration of the rock, facilities are provided to draw off any water which may collect. Extreme care had to be displayed in connecting the lengths of piping, so that there might be no leakage, in which event, of course, the pressure of the air would drop and thereby incapacitate the signal.