Nautical charts . coast. Fog whistles and bell buoys aremaintained at many places. Submarine bells haverecently been introduced at a number of points alongthe Atlantic coast, and vessels may be equipped to receivethese submarine signals transmitted through the water,which indicate also the general direction from whichthe sound comes. Need of vigilance. Too great importance cannot beattached to frequent verification of positions by the bestavailable means, particularly when approaching theland. Neglect of this or overconfidence has causedmany disasters. A notable instance was the loss of oneof
Nautical charts . coast. Fog whistles and bell buoys aremaintained at many places. Submarine bells haverecently been introduced at a number of points alongthe Atlantic coast, and vessels may be equipped to receivethese submarine signals transmitted through the water,which indicate also the general direction from whichthe sound comes. Need of vigilance. Too great importance cannot beattached to frequent verification of positions by the bestavailable means, particularly when approaching theland. Neglect of this or overconfidence has causedmany disasters. A notable instance was the loss of oneof the largest Pacific steamers on the coast of Japan inMarch, 1907. In the afternoon of a clear day thisvessel ran on to a well-known reef about a mile from alighthouse, resulting in the total loss of vessel and cargovalued at three and a half million dollars. The captainwas so confident of his position and that he was givingthe reef a sufficient berth that he laid down no bearingson the chart and took no FIG, 47. FIELDS PROTRACTOR AND PARALLEL RULER IN USE ON A BEARING OF A LIGHTHOUSE. (141) Instruments 143 Instruments. The principal instruments needed foruse with charts are; dividers for taking off distances andlatitudes and longitudes, parallel ruler for transferringdirections to or from a compass rose and for taking offor plotting the latitude on a mercator chart, protractor of180 degrees for reading the angle with the meridian of anydirection or for laying off on the chart any given angle withthe meridian, and three-arm or other full-circle protrac-tor for plotting a position by the three-point problem. Parallel rulers on the principle of Fields are stronglyrecommended for chart work, as they combine in asingle instrument the advantages of a parallel rulerand a 180-degree protractor. Any direction can beread or laid off by simply moving the parallel rulerto the nearest projection line, which is a process notonly more convenient than referring to th
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