Steamship traffic cannot be carried on with financial success by daylight and in fair weather only, so it became necessary to distribute beacons around the indented shores. This procedure was rendered additionally necessary owing to the formidable character of many of the dangers besetting navigation, in the form of shoals, projecting ridges, and submerged reefs, quite as terrifying to the master of a fresh-water ship as similar dangers on an ocean-swept coast. At the same time, however, one would not expect to find examples of lighthouse engineering comparable with the great sea-rock lights rearing above the ocean, such as the Minot’s Ledge, Dhu-Heartach, or Bishop’s Rock. On the other hand, the uninitiated might conclude that buoys and small lights, such as indicate the entrance to harbours, would fulfil requirements. So they would but for two or three adverse factors. These lakes are ravaged at times by storms of great violence, which burst with startling suddenness. Fogs also are of frequent occurrence, especially in the spring and autumn, often descending and lifting instantly like a thick blanket of cloud. But the most implacable enemy is the ice. The engineer can design a tower which will withstand the most savage onslaughts of wind and wave with comparative ease, at, relatively speaking, little expense; but the ice introduces another factor which scarcely can be calculated. The whole of these lakes are frozen over during the winter to such a thickness as to defy all efforts to cut a channel, becoming, in fact, as solid as terra firma. [Illustration: _By permission of the Lighthouse Literature Mission._ A LIGHTHOUSE ON THE GREAT LAKES IN THE GRIP OF WINTER. This tower marks the Racine Reef in 20 feet of water near the entrance to Racine Harbour on the west coast of Lake Michigan.] In the spring this armour cracks and breaks up like glass shattered with a hammer. It then becomes the sport of the currents, which in many places sweep and swirl with enormous force round the headlands and spits projecting into the lake. This action sets the ice moving in stately majesty, but crushing everything that rears in its way, or piling and breaking against the obstruction. Ice-shoves, ice-jams, and ice-runs, are the three forces against which the engineer has to contend, and at places his efforts are so puny as to be useless. The ice, if it collects across one of the outlets so as to form a massive dam reaching to the lake-bed, immediately causes the level of the lake to rise; and when at last the barrage breaks, then the water is released in a mad rush.