In foggy weather when ships are “on soundings”—that is, where the water is shallow enough to permit of the easy use of a line with a weight attached for measuring its depth—careful navigators invariably use the “lead line” constantly. [Illustration: SOUNDING BY MACHINE _A glass tube with the upper end closed and the lower end open is lowered in a special case to the sea bottom, and then brought to the surface. As the tube descends, the water compresses the air in the tube, and gradually creeps up inside. The inside of the tube being of ground glass the water leaves a mark showing how far it has entered the tube. By laying the tube on a special scale the depth to which the glass was carried can be gauged. There are other methods not greatly dissimilar from this._ ] This tells them not only how deep the water is, but by putting tallow or soap on the bottom of the lead weight they bring up sand or mud or shells from the bottom. With this and the depth, a line is drawn on tracing paper on the same scale as the chart. Along this line these soundings and the kind of mud or sand the lead brings up are marked, at intervals corresponding to the distance the ship has sailed between soundings. The chart is printed with the depth of the water in fathoms and with the kind of bottom that will be found. After the navigator has compiled his data for a few miles the tracing paper with the line on it can be moved about over the chart, and if care has been taken in sounding and watching the speed and direction of the ship, the navigator will find the place on the chart where his series of soundings will match the printed soundings. Then he will know very accurately where he is, even if it be a fog-enshrouded night. Many, many important aspects of these three vital subjects have been completely passed over in this short chapter. If, however, I have been able to explain a little of the subjects, and if, particularly, I have quickened the interest of any of my readers in them, my purpose has been served. Going to sea is not so difficult as many people ashore are prone to think. But becoming a thorough seaman and a thorough navigator is not so simple, perhaps, as to become adept at much of the work that occupies men ashore. CHAPTER XI LIGHTHOUSES, LIGHTSHIPS, AND BUOYS Just as the origin of ships is lost in the darkness of shrouded time, so is the origin of lighthouses lost. Perhaps to guide returning fishermen who all day and into the night had spread their nets or cast their spears for food, the women of some savage tribe of long ago built bonfires on the beach. Still that is a custom among simple folk who live hard by the sea and secure their livelihood from it.