The “flashing light” is that which shows alternately two flashes and two eclipses, or more, in the interval of a minute.
The “flashing light,” the “intermittent,” and the “double lights in one tower” were all first proposed and introduced into Scotland by the late Mr. R. Stevenson.
The lustre of the “revolving light” gradually increases to a maximum, and diminishes to a minimum, until wholly eclipsed, at equal intervals of half a minute, one, two, or three minutes, and sometimes thrice in a minute.
We designate it an “intermittent light” when the ray suddenly appears, remains visible for a moment, and afterwards is again suddenly eclipsed for a brief interval.
With this scientific arrangement before us, it seems strange to recollect that even so lately as the year 1816, the Isle of May light, in the Firth of Forth, consisted of nothing better than a coal-fire. Nor had England made any greater progress in the art of illumination, for the magnificent tower of the Eddystone, says Mr. Stevenson, about fifty years after it came from the hands of Smeaton, could boast of no better light than that derived from a few miserable tallow candles. Nay, so lately as the year 1801, the light at Harwich, in addition to the coal-fires, had a flat plate of rough brass on the landward side, to serve as a reflector! Such methods, continues Mr. Stevenson, were most imperfect, not only in point of efficiency and power, but also as respects the distinction of one light from another; an object which, on a difficult and rugged coast, may be considered as of almost equal importance with the distance at which the lights can be seen.[16]
It must also be remembered that too great a multiplicity of lights would not be less dangerous than a deficiency in number. Were the littoral too abundantly illuminated, the effect produced on the navigator would be that of a continuous and confused line of fire. He would be dazzled by the blaze, and unable to determine the particular point to which he should steer his vessel. Before the Royal Commission of 1861, one witness actually gave it as his opinion that there were too many lights on the English coast, and that the consequence was an increase of collisions, a neglect of the lead, and continual shipwrecks. He added, however, that without the increase of light, steamers could not run in and out of ports at night. The extent of illumination being necessary, the only method of reducing the danger of confusion to a minimum is that adopted by our engineers—a clear and distinct variety of lights.
