Find the meridional difference of latitude in each of the To find the middle latitude, having given the latitude from and latitude in. The names being supposed to be alike, that is, both north or both south. Add together the two latitudes, and take half the sum; the result is the middle latitude. When the names are unlike, the mid. lat. (which is seldom required but for obtaining the departure) should be found by means of a table; but in this case it may perhaps be as well to avoid the use of the middle latitude in any of the common problems in navigation. EXAMPLES. 17. Find the middle latitude, having given latitude from 3° 42′ N., and latitude in 13° 52′ N. Rule (d). To find the difference of longitude, having given the longitude from and longitude in. (1.) When the longitude from and longitude in have like names; that is, are both east or both west. Under longitude from put longitude in, take the difference, and reduce the same to minutes; place E. or W. against the remainder according as the longitude in is east or west of longitude from; the remainder will be the difference of longitude. (2.) When the longitude from and longitude in have unlike names, that is, one east and the other west. Take the sum of the two longitudes, reduce it to minutes, and attach E. or W. thereto according as the longitude in is east or west of the longitude from; the result is the true difference of longitude. NOTE. If the difference of longitude found by this rule exceed 180°, it must be subtracted from 360°, and the remainder brought into minutes must be considered the difference of longitude, with the contrary letter attached to it. EXAMPLES. 20. Find the difference of longitude, having given the longitude from = 110° 42′ W., and longitude in 100° 42′ W. 21. Find the difference of longitude, having given long. from 12° 10' E., and long. in 2° 45′ W. Find the difference of longitude in each of the following To find the latitude in, having given the latitude from and true difference of latitude. (1.) When the latitude from and true difference of latitude have like names. To the latitude from, add the true difference of latitude (turned into degrees and minutes, if necessary); the sum will be the latitude in, of the same name as the latitude from. (2.) When the latitude from and true difference of latitude have unlike names. Under the latitude from put the true difference of latitude (in degrees and minutes, if necessary): take the less from the greater; the remainder, marked with the name of the greater, is the latitude in. EXAMPLES. 28. Find the latitude in, having given the latitude from 42° 30′ N., and true difference of latitude 342' N. 29. Find the latitude in, having given the latitude from 2° 40′ S., and true difference latitude 342′ N. Find the latitude in, in each of the following examples: To find the longitude in, having given the longitude from and the difference of longitude. (1.) When the longitude from and diff. long. have like names. To the long. from, add diff. long. (turned into degrees if necessary); the sum will be long. in, of the same name as long. from. (2.) When the long. from and diff. long. have unlike names. Under long. from, put diff. long. (in degrees and minutes, if necessary); take the less from the greater; the remainder, marked with the name of the greater, is the long. in. NOTE.-If the long. in, found as above, exceed 180°, subtract it from 360°, and attach to the remainder the contrary name to the one directed in the Rule. EXAMPLES. 36. Find the long. in, having given long. from 38° 42′ W., and diff. long. 384.5' W. Find the longitude in, in each of the following examples: THE Compass card is represented above; each quadrant is divided into eight equal parts, called points; each point therefore contains 11°15'. The names of the points are formed as follows: N.E. Middle point between N. and E. is formed by putting these N.N.E. The points of the compass are frequently referred to with respect to their position to the right or left of the cardinal point towards which the spectator is looking; thus, N.E. is |
