The mariner, in pursuit of his daily business, is exposed to dangers innumerable. In mid-ocean, for the most part, he need not fear them particularly, because he has plenty of sea-room in which to navigate his ship, and in case of thick fog he can ease up until this dreaded enemy lifts or disperses. But in crowded coastal waters his position is often precarious, for he may be menaced by lurking shoals or hidden reefs, which betray little or no indication of their whereabouts, and which may be crossed with apparent safety. If the ship blunders on in ignorance, it is brought up with a thud as it buries its nose in the sucking sand, or gives a mighty shiver as it scrapes over the rocky teeth, perhaps to be clasped as in a vice, or to be battered and broken so fearfully that, when at last it tears itself free and slips off into deep water, it can only founder immediately. Here, if fog blots out the scene, the ship is in danger of being lured to certain destruction by currents and other natural forces, since the captain is condemned to a helplessness as complete as of a blind man in a busy street. It is not surprising, then, that the captain, as he approaches or wanders along a tortuous shoreline, scans the waters eagerly for a glimpse of the guardian monitor, which, as he knows from his reckonings and chart, should come within sight to guide him on his way. The danger-signal may be one of many kinds--a misty, star-like glimmer thrown from a buoy dancing on the waves, the radiant orb from a lightship bobbing up and down and swinging rhythmically to and fro, a fixed flare-light, or dazzling, spoke-like rays revolving across the sky. If sight be impossible owing to fog, he must depend upon his ear for the measured tolling of a bell, the shriek of a whistle, the deep blare of a siren, or the sharp report of an explosive. When he has picked up one or other of these warnings, he feels more at ease, and proceeds upon his way, eyes and ears keenly strained for warning of the next danger ahead. The lighthouse is the greatest blessing that has been bestowed upon navigation. It renders advance through the waters at night as safe and as simple as in the brilliancy of the midday sun. But for these beacons the safe movement of ships at night or during fog along the crowded steamship highways which surround the serrated shores of the five continents would be impossible. It is only natural, therefore, that the various nations of the world should strenuously endeavour to light their coasts so adequately that the ship may proceed at night as safely and as comfortably as a man may walk down an illuminated city thoroughfare.