N reference to the military protection of our coasts, the civilian is frequently warned of the necessity of maintaining more than one line of defence; a similar necessity exists as regards their complete and satisfactory lightage. We know, too, that at one point a battery is erected; at another, a simple earthwork is pronounced sufficient; at a third, the eye ranges over an intricate combination of forts. The same variety exists in the disposition of those coastdefences which are designed in the interests of secure and peaceful navigation. Follow, with the mind's eye, the long coast-line of our country, and how many differences we shall note in the situation of its lighthouses, in their mode of construction, their elevation, their system of illumination. Each pharos has, as it were, a speech of its own; each addresses, in significant language, the seaman who turns to it for advice or warning. This points out the entrance to a commodious haven, where, after being much tossed by unquiet waves, the weary mariner may repose in safety; that indicates the site of a perilous

VARIETY OF LIGHTS.

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rock or sand-bank, on which a storm-driven vessel must assuredly perish. Here we see a noble tower, whose genial rays are visible at a distance of twenty-seven nautical miles; there burns a steady light, whose extent of illumination is restricted to five miles. One is a fixed light, glowing constantly like a brilliant star; another, more mysterious, suddenly flashes forth from the deep darkness, flings over the sea its arrow of flame, and then is again extinguished, to reappear, a few moments later, in the same strange and impressive manner. Nor are all lights of an uniform colour. Some are red, with an intense ruby-like splendour; others white; others, again, are blue or green. This variety in the range and aspect of the "beacon-fires" has, like the variety in the size and position of our forts and batteries, a special object.

The system of lightage generally adopted, says M. Renard, consists in surrounding the coast with three lines of defence; the outmost being composed of lighthouses with a very extensive range. It has justly been deemed of the highest importance to signal to the mariner the proximity of the land, since it is in the waters near the coast that navigation is exposed to the greatest dangers. The littoral presents a number of capes, promontories, and headlands, more or less projecting beyond the general level, as well as islets, and reefs, and shallows, which require to be carefully avoided. Now, lighthouses of the first class, as we may call them, or "sea-lights," are usually planted on these promontories or rocks; and along the British shore they are so arranged that it is impossible, except in a dense fog, to arrive in its neighbourhood without catching sight of one or more of them.

THE LIGHTHOUSE ON THE ROCKY HEADLAND.

When he has overpassed the first line of defence, the navigator encounters a second circle-"secondary-lights" -composed of lighthouses of the second and third orders, indicating secondary capes, reefs, and sand-banks, to which it is prudent to give a good offing. When the mouth of a river or the entrance of a port is only accessible by narrow channels, whose direction an experienced and veteran pilot can hardly determine by night, other lights of the same class are placed in the line of the channel, and point out the exact course which should be taken.

Finally, when the ship has arrived near the port which is the goal of her voyage, she perceives lights

THE FIVE LIGHTS.

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"harbour-lights"-upon its piers or breakwaters, which guide her to her much-wished-for berth.

When the best positions for illumination have been selected, the most difficult task is, or rather was, to provide for their easy distinction, so that the sailor may not be misled by too close a resemblance of one to another. Suitable variations and modifications have been, fortunately, supplied by the valuable labours of Fresnel, and of the engineers who have followed in his track.

At first, however, the embarrassment was considerable. Thus, the code laid down by the celebrated French Commission in 1825, admitted of only three characters for lighthouses of the first order: the "fixed light," the "revolving minute light," and the "revolving half-minute light." But it was soon discovered that merchant seamen did not sufficiently heed the differences observed between the intervals of the appearance and disappearance of the latter lights; and the number of lighthouses, moreover, having multiplied beyond all prevision, it became absolutely indispensable to allow of a greater number of distinctive characters.

Now-a-days we recognize five: the "fixed light," the "flashing light," the "revolving," the "intermittent," and the "double lights in one tower."

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.

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THEIR RECENT INTRODUCTION.

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.'

*

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 * Stevenson, On Lighthouses," pp. 60, 61.