SAILINGS, the to•lmical name in navigation for the various modes of determining the amount or dir •tion of a ship's motion. or her position after having sailed a given dis tance in a given direct ion. The direction of a ship's motion is her course. and is expressed in terms of the angle between the line of direction and the meridian; the length of her path is the dish; net ; the distance in nautical miles. made good to the e. or w., is the den/Hae, and is measured a parallel; the d;:rereoce of latitude is an arc of the meridian i hti-rcupted by the parallels, one of which passes through the place sailed from, the other lbriaigh the place sailed M: and the diprenee rf longitude is an arc of the equator intercepted by meridians through the same two places. It will at mice be seen that if it shit sails alone- a meridian, the difference of latitude becomes the course., and there is no a •oartnre or difference of longitude; and that if it sails ;110117 a parallel the departure v•i.I he the same as the and dare will he no difference of latitude. The two genetil oliestions which present themselves to the navigato• for solution a•e 1. Given the course and distance from one place in given latitude and longitude to another phi a•, find the latitude and longitude of the other; and 2. Given the latitude and longitude if places, find the and list aunee from the one to the other. The SIM plest way i such problems eau be solved is by the method known as plane sailing, a method, however, which is only roughly approximate, assuming, es it does, that Vie sur face of the sea is a plane; it is consequently applicable only to short distances and l w latitudes where the meridians arc uearly parallel. According to "plane suiting," the elements of a ship's path are represented by a right-angled plane triangle, as ABC (fig.), where AB is the distance, the angle BAC the course, AC the difference of latitude (AC being a portion of a meridian, and BC of a parallel of latitude), and BC the departure. The two problems given above are in this method merely simple cases of the resolution of a right-angled plane triangle (see TmooxoNamtv), for it' the course and distance are given, the thy; of lat. = distance X cos. of course, and dep. = (list. X sin. of course;
while the idea of dif. of long., as distinct front dep., is quite inadmis sible, since the method presupposes that the ship is sailing on an absolutely Bat plain. If the ship does not stand ou one course, but changes from time to time, the calculation of her final position may be effected, either by the previous method, repeated for each change of course, or more conveniently, by the method of tracerse sailing. This method consists in the resolution of a ship's course thstauce into two courses and distances, the courses being in the direction of some of the four cardinal points of the compass; thus, a ship which has sailed s.w.-by-s. for 24 in,, lies made 20 in. of soothing, and 13.3 in. of westing. The traverse table has consequently six columns, the first containing the courses; the second, the corresponding disianeRE: while the third and fourth contain the difference of latitude for each course, which. if n., is put in one column, and if s. into the other; the fifth and sixth columns, marked recpec uccly e. w., contain in a similar manner the derail ure for each course. When the table has been made out for the various courses and distances, the columns of di f. of lat. and departure are summed up, and the difference between the third and fourth, and between the fifth and sixth columns, gives the dif. of let. and departure between the place sailed from and the place arrived at, from which the course and distance made good can be calculated as before. When a ru:•ent interferes in any way. cither by accel erating or retarding the ship's motion, its effect is estimated as in traverse sailing, as if it were one course and distance, the set of the current being the course, and its drift. i.e., its rate per hour multiplied by the number of 110111's it Naas affected the ship, the distance.