Imagine a sandy shoal marked only by a white-fringed breaker. The water rushes over it in swift and constantly varying currents, and if there is a capful of wind anywhere on the sea, it becomes an instant menace to the mariner. The shore may be ten or twenty miles away, so far that a land-light would only lure the seaman into peril, instead of guiding him safely on his way. A lightship is always uncertain; the first great storm may drive it from its moorings and leave the coast unprotected when protection is most necessary. Upon such a shoal, often covered from ten to twenty feet with water, the builder is called upon to construct a lighthouse, laying his foundation in shifting sand, and placing upon it a building strong enough to withstand any storm or the crushing weight of wrecks or ice-packs. It was less than twenty years ago that sea-builders first ventured to grapple with the difficulties presented by these off-shore shoals. In 1881 Germany built the first iron cylinder lighthouse at Rothersand, near the mouth of the Weser River, and three years later the Lighthouse Establishment of the United States planted a similar tower on Fourteen-Foot Banks, over three miles from the shores of Delaware Bay, in twenty feet of water. Since then many hitherto dangerous shoals have been marked by new lighthouses of this type. [Illustration: Fourteen-Foot Bank Light Station, Delaware Bay, Del.] When a builder begins a stone tower light on some lonely sea-rock, he says to the sea, "Do your worst. I'm going to stick right here until this light is built, if it takes a hundred years." And his men are always on hand in fair weather or foul, dropping one stone to-day and another to-morrow, and succeeding by virtue of steady grit and patience. The builder of the iron cylinder light pursues an exactly opposite course. His warfare is more spirited, more modern. He stakes his whole success on a single desperate throw. If he fails, he loses everything: if he wins, he may throw again. His lighthouse is built, from foundation caisson to lantern, a hundred or a thousand miles away from the reef where it is finally to rest. It is simply an enormous cast-iron tube made in sections or courses, each about six feet high, not unlike the standpipe of a village water-works. The builder must set up this tube on the shoal, sink it deep into the sand bottom, and fill it with rocks and concrete mortar, so that it will not tip over. At first such a feat would seem absolutely impossible; but the sea-builder has his own methods of fighting. With all the material necessary to his work, he creeps up on the shoal and lies quietly in some secluded harbour until the sea is calmly at rest, suspecting no attack. Then he darts out with his whole fleet, plants his foundation, and before the waves and the wind wake up he has established his outworks on the shoal. The story of the construction of one of these lighthouses will give a good idea of