On all the largest steamships there are besides a captain and chief officer, three second officers, one third and one fourth officer. The second officers are known as senior second, junior second and extra second, and each, like the chief officer, is a duly qualified master, capable of taking the ship around the world if need be. The general duty of the second officer is the navigation of the ship under the captain's directions. Each of these officers stands a four hours' watch on the bridge, and each during his tour of duty has, as the captain's representative, direct charge of the ship. The third and fourth officers stand a watch of six hours, alternating with each other, and, there are, therefore, always a second and third or fourth officer on watch at the same time. Although in rough weather it is work that tests the strength and tries the nerves of the strongest man, no officer can leave the bridge while on watch, and should he violate this rule, he would be dismissed at once. In addition to his watch the third officer has charge of all the flags and signals by night and day, and he also keeps the compass book, while the fourth officer, besides his work on the bridge, has charge of the condition of the boats. Observations are taken every two hours, as on an ocean greyhound, rushing over the course between America and Europe at the rate of twenty miles an hour, it is of the first importance that the ship's position should be known at all times. Fog may come down at any moment, and observations not to be obtainable for several hours. The positions of more than one hundred stars are known, and by observing any of these the ship's whereabouts can be ascertained in a few minutes. Of course, the "road" becomes more or less familiar to a man who crosses the ocean along the same route year after year, yet this familiarity never breeds contempt or carelessness, for no man knows all the influences that affect the currents of the ocean, and while you will find the current in a given place the same forty times in succession, on the forty-first trip it may be entirely changed. Now and then a big storm that has ended four or five hours before a liner passes a certain point may give the surface current a strong set in one direction, and there is no means of telling when these influences may have been at work save by taking the ship's position at frequent intervals.