EXPLANATION OF NAUTICAL TERMS, 23 EXPLANATION OF NAUTICAL TERMS, USED IN WORKING A DAY'S WORK. The Course is the angle the ship's track makes with the meridian, and is expressed either in points or degrees. The distance is the number of miles a ship sails on a direct course between any two places. The difference of latitude, as explained at page 20, is the arc of the meridian, intercepted between the parallel of the place left, and that arrived at. The departure is the distance of the ship from the meridian of the place sailed from, reckoned on the parallel of the latitude arrived at. If a ship's course be due north or south, she sails on a meridian, and therefore makes no departure, and the distance. run will be equal to the difference of latitude. The same observation applies to the course if due east or due west, the ship then sails on the equator, or on the same parallel of latitude and therefore makes no difference of latitude and in this case the distance run is equal to the departure. On all other courses she will make both difference of latitude and departure. When the course is 4 points, or 45 degrees, the difference of latitude and departure are equal. When the course is less than 4 points or 45 degrees, the difference of latitude exceeds the departure, but when it is more than 4 points or 45 degrees, the departure exceeds the difference of latitude. 24 EXPLANATION OF NAUTICAL TERMS. THE LOG BOOK OR JOURNAL. This should contain a correct register of all that occurs on board of a ship, both in port and at sea. That part of the log book which relates to the transactions on board the ship in port, is called the harbour log. That part relating to the navigating of the ship, and to the various occurrences which take place at sea, is called her sea log. The duty therefore of the navigator commences at the time of his taking his departure, when he is leaving the land, by which is meant taking the exact bearing of some known point or place, the true latitude and longitude of which is known, together with the estimated distance of the said point or place from the ship. The former is obtained by compass, the latter is commonly estimated by the eye. Great care must be taken in working out the first day's work after leaving land, putting down the bearing and distance of the departure, (as a course and distance) in the table, to make use of the opposite point of the compass to that bearing, and also to make the proper correction for variation. It will be advisable for the pupil to read attentively the following DIRECTIONS FOR WORKING A DAY'S WORK. Prepare a table similar to that used in Traverse Sailing, in this enter the several courses steered, corrected for variation and lee-way, and against each course place the whole distance run while on that course. Then find the difference of latitude and departure answering to each course and distance, and put them down in their respective columns. From them find the difference of latitude and departure made good upon the day's run, as in Traverse Sailing. With this difference of latitude and departure, the true course and distance made good are to be found in the usual manner. When the variation of the compass is given in degrees, it will be more convenient to correct the courses for lee-way only, and with these courses and their respective distances, to find the difference of latitude and departure, and thence the compass course, and the distance made good during the whole day's run. This course being corrected for variation, will give the true course, with which, and the distance already found, the true difference of latitude and departure may be readily obtained, and thence the true course and distance as before. Having the difference of latitude, the latitude the ship is in is to be found by the following rule. Rule: When the latitude left and the difference of latitude are of the same name, their sum will be the latitude in, but when of contrary names, their difference will be the latitude required, this latitude will always be of the same name with the greater quantity. Ex. A ship from latitude 50° 3′N. sails in a northerly direction till her difference of latitude is 300 miles, required her latitude in. The difference of longitude is to be found by Middle Latitude or Mercator's Sailing; and the longitude in, by the following rule. E Rule: When the longitude left and the difference of longitude are of the same name, their sum will be the longitude in, unles the sum exceed 180°, when that sum must be taken from 360° and the remainder will be the longitude in, of a contrary name to the longitude left; but when the longitude left, and the difference of longitude are of contrary names, their difference will be the longitude in, of the same name with the greater. Ex. A ship from longitude 175° 5′E. sails eastward until her diff. of long. is 350 miles required her longitude in. Having thus found the latitude and longitude the ship is in, her place may be pricked off on the chart; and the bearing and distance of the intended port, or of any place whose latitude and longitude are known, may be found by Case 1 in Mercator's, or Middle Latitude Sailing. The bearing thus found will be the true bearing, if therefore, the compass bearing be required, the variation must be allowed according to the rules given under the head of variation of the compass. The setting of currents are to be corrected for variation only, and entered as courses in the traverse table, the drift being taken as a distance. When a ship is lying-to, the middle point between those on which she comes up and falls off, is to be taken for her apparent course, upon which the lee-way and variation are to be allowed to find the true course. The following table* will represent the log-book or Journal, and will sufficiently explain how the corrections on the different courses are to be made, as well as the usual method of keeping a Journal. Is the angle contained between the course towards which the ship's head is directed, and the course she really describes through the water. When a ship is close hauled, and the wind blowing fresh, |