On May 19th the sun's semi-diameter as given in the Nautical Almanac is 15o 50'1. 123. By the horizon.-Place the zero of the vernier to the zero of the arc, and bring the true and reflected horizons in one straight line, then what the sextant shows will be the Error, additive if the reading is off the arc, but subtractive if it is on. MERCATOR'S CHART. TO FIND THE LATITUDE AND LONGITUDE OF ANY PLACE. 124. To find the Latitude.—With the compasses measure the distance between the place and the nearest parallel of latitude; now place one foot of the compasses at the end of this parallel (in the margin of the chart,) and let the other foot rest upon the scale upon the same side of the parallel as the given place, this when read, will be its latitude. 125. To find the Longitude.—Measure the distance between the place and the nearest meridian, and take it to the scale lying at the end of your meridian, now in the same way as for the Latitude read what this will shew, and the result will be the Longitude. Ex. 1.— Find the Lat. and Long. of West Point, Anticosti. 662. TO FIND THE PLACE CORRESPONDING TO A GIVEN LATITUDE AND LONGITUDE. 126.-Place one foot of your compasses on the given lat. as shewn by the scale, and measure the distance between it and the nearest parallel; take your parallel rulers and having placed the edge upon this parallel, move it in the direction of the given lat. until it is at the distance shewn by the compasses from the parallel; now taking your longitude upon the scale, measure the distance between it and the nearest meridian, and placing one foot of the compasses upon the same meridian and against the edge of the rulers, then, where the other foot falls against the edge (in the direction of the long.) will be the position required. Give the soundings upon which the following Latitudes and Longitudes fall. TO FIND THE COURSE AND DISTANCE BETWEEN TWO PLACES. 127. To find the Course.-Lay your rulers so that the two places appear upon its edge, move the rulers to the centre of the compass and the point upon which it lies will be the course; if the compass is Magnetic the course found will be magnetic, but if True the course will also be true, and may be brought into the magnetic course by applying the variation the reverse way, that is, East to the left and West to the right. 128. To find the Distance.-If the distance is not too long, place a foot of the compasses upon each of the two places, and take them to the scale at the latitude side of the chart, and having placed them so that their centre will be over the middle latitude (roughly guessed) then the distance will be the number of miles spanned by the compasses: if however, the distance is too long to be taken at one stretch, find the rough middle latitude, and over this, on the scale, take as many miles in your compasses as you may find convenient, see how often this distance will go between the two places, and measure off the remainder, if any, and these distances taken together will be the distance required. Find the Course and Distance between the following places. Ex. 11. Cape Race. From Scatteri 12.- 66 St. Pauls to Ex. 18. From Lat. 43° 10′ N. Long. 62° 27′ W. to Cape Ann. 19.- (6 Island, S. W. point. Lat. 42° 24' N. Long. 56° 18′ W. to Seal Island. TO FIND THE POSITION OF THE SHIP BY CROSS BEARINGS. 129.-Lay off your bearings from the points given, and where the lines cut one another will be the position of the ship. If the chart has a True Compass only, the Variation and Deviation must be allowed to the compass bearings in the same way as in a Day's Work. TO FIND THE POSITION OF THE SHIP BY TWO 130. Lay off the bearings from the object observed; place your parallel rulers upon the course steered during the interval, and now with the distance run in your dividers, slide your rulers along the lines of bearings until one leg of the dividers falls upon each line, then the points indicated will be the positions of the ship when the bearings were taken. In finding your position by this method, you should sail on until you have altered the bearing of the object not less than three points. TO FIND THE COURSE TO STEER IN A CURRENT. 131. Lay off in pencil the course it is required to make, have a dot anywhere upon this line and from this lay off the current; from the dot and along the line of current prick off the drift, and now having the rate of sailing in your compasses, place one foot at the end of the drift and mark where the other falls upon your line of bearing, lay the edge of your parallel rulers against these two marks, and having taken it to the compass, you will have the course required. THE COMMERCIAL CODE OF SIGNALS. 132. Code Signal.—When this is hoisted under the Ensign it signifies that the vessel is using the Commercial Code, but if it is hoisted singly it is then used as an "answering pennant," denoting that the last signal has been understood. |