are the parallel rulers, the dividers, and the course protractor, shown in Fig. 22. Provided with this outfit in addition to a lead pencil and pad for notes, almost any ordinary problem in which the chart is used may be solved. Although some practice is required before proficiency is attained, the manipulation of these accessories to the chart is very simple and should be readily acquired by any person of ordinary intelligence.

45. The parallel ruler is usually made of ebony or gutta percha. The two parts are connected by crosspieces of brass working on pivots in such a manner that they may be spread apart or pushed together and still remain parallel to each other. They are used for the purpose of transferring the direction of a bearing, or course, to the nearest compass diagram,

or vice versa. For instance, in Fig. 23, if it is required to find the bearing between a and b, the edge of a closed parallel ruler is laid between the two places and then the upper part of the ruler is pushed forwards to the center c of the nearest compass diagram and the bearing read off immediately. In some cases, it may be necessary to take several steps with the ruler in order to reach the diagram, but the operation in itself is so simple as to need no further explanation. The

main point, however, is to preserve the parallelism of the last step with the first.

46.. Several patent parallel rulers are now on the market, among which may be mentioned the Sigsbee, the Field, and the Kay rulers. The main advantage of these over the ordinary parallel ruler is their greater spread, or the distance to which the rulers can be separated, thus doing away with the necessity of many steps in transferring courses and bearings over the chart. Another advantage is that shuffling may be made straight forwards, while the ordinary ruler has a diagonal motion due to the single cross-pieces connecting the two parts.

FIG. 24

47. The dividers, shown in Fig. 24, are used to lay off and measure distances. They should be made of well-tempered steel and their points should be sharp but not too fine. When using the dividers to lay off a distance into a number of equal parts, they should be held at the top between the thumb and forefinger and the spaces stepped off by turning the instrument alternately to right and left. When laying off a distance in this manner, great care must be exercised not to press the divider points into the chart; they should be turned lightly and the final point indicated by a pencil mark, lightly applied.

48. The course protractor is shown in Fig. 25. The outer edge is a semicircle, with a center at o, and is divided into degrees and half degrees and graduated so that angles

The pro

can be read both ways. Thus graduations may be read from a to b or from b to a, as indicated by the arrows. tractor is used for laying off or measuring courses or bearings;

it should be made of celluloid or metal and have a radius of at least 3 inches. When using the protractor, it must be placed so that the line o a, o b, or o c will coincide with the line forming

one side of the angle to be laid off or measured and the center o must be at the vertex of the angle. For instance, if it is required to find the bearing between the two points a and b, Fig. 26, a straightedge, such as a parallel ruler, should be placed between the two points, as shown; then the protractor placed along the ruler, with its center o on one of the meridians, and the bearing read off as indicated by the number of degrees contained in the arc c d reckoned from the meridian-in this case about N 57° W, or simply 57°.

Or, the two points may be connected with a pencil line drawn lightly when the center of the protractor placed at the point of

intersection between the pencil line and one of the meridians will give the number of degrees required. The use of a straightedge, however, is preferred to pencil marks drawn on the chart. The protractor may be placed on any other position, provided its center is exactly at the intersection of meridian and line of bearing. It must be remembered that the course or bearing thus found is true, not magnetic.

49. In general, to find the course and distance between any two points on the chart, the edge of a ruler is placed so that it passes through and connects the points. The ruler is then

shifted to the nearest compass rose when, as already explained, the course, either true or magnetic, is read off. Usually the magnetic course is taken from the rose; then by applying to it the deviation, according to forthcoming directions, the course to steer by compass is obtained. To get the distance between the two points, the ruler is placed once more over them and the distance measured, using a suitable unit taken, by the dividers, from the scale of nautical miles. This unit is stepped off along the edge of the ruler, as shown in Fig. 27, by holding the ruler firmly with the left hand while the right hand is used to manipulate the dividers. In cases where the distance between the two points considered is small and within the limit of the scale, it may be spanned by the dividers and transferred to the scale when the required distance is obtained quickly and conveniently.

THE LEAD

50. The operation of measuring the depth of the water and investigating the character of the bottom is called sounding. The instruments used for this purpose are the lead and the sounding machine. There are three kinds of leads, viz., the hand lead, the coasting lead, and the deep-sea lead. All sounding leads are similar in form to the one shown in Fig. 28, being widest at the lower end a, which is hollowed out for the reception of a lump of tallow. Filling this cavity with tallow is called the arming of the lead and the purpose of the tallow is to bring up a specimen of the bottom that it touches, so that the quality of the ground struck by the lead whether it is sand, mud, or gravel, may be compared with the description of the bottom given on the chart or in sailing directions, and the vessel's position therefrom approximately determined.

FIG. 28

51. The hand lead weighs from 4 to 14 pounds and is therefore readily thrown by hand. It is well adapted for use in shallow water and for soundings in channels, rivers, and har