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degree or point on the circumference. Then move the ruler, step by step, until the edge passes through the object, when the line drawn along the edge will represent one of the bearings. The ship will then be somewhere on the line. Proceed similarly with the other bearing. Now, the ship will be somewhere on this line also, and since the only common point of two lines intersecting each other is at their point of intersection, the position of the ship on the chart must necessarily be at the point where the two bearings intersect.

64. It is evident that the objects selected for crossbearings should be so situated that the lines of bearings do not intersect at a very acute angle, since the point of intersection in such cases is somewhat doubtful. To obtain good results, the angle between the bearings should be as near as possible to 90°, or 8 points.

EXAMPLES FOR PRACTICE

1. Find on Plate I the approximate true course from Bermuda to Sandy Hook? Ans. N 42° W, or N WN.

2. A ship sails a distance of 240 miles from Sandy Hook, steering a true course SE by E. Find on Plate I her latitude and longitude in. Ans.-The ship's position will be found to be at X, in latitude 38° 15′ N and longitude 69° 50′ W.

3. A bearing was taken of the westernmost end of Bermuda Islands E SE (true); calculated distance=30 miles; from this position the following true courses and distances were run: N E, 240; WSW W, 120'; N by E, 250'; S E by S, 120'; W N W, 300; SS WW, 210'; W 120. Required, by construction, the latitude and longitude in, and the course and distance from the position arrived at to Sandy Hook. Ans. When properly laid out according to instructions given in preceding articles, the result should be approximately as represented on Plate I, whence,

Lat. in=36° 11′ N.

Long. in 72° 15′ W.

Course to Sandy Hook=N 18° W.

Distance to Sandy Hook=250 miles (nearly).

CONVENTIONAL SIGNS AND ABBREVIATIONS USED ON CHARTS

65. On charts issued by the United States Hydrographic Office, Washington, D. C., explanatory notes are usually given regarding abbreviations and signs used. On American and most foreign charts, the following representations are, as a rule, adhered to.

66. Soundings on plain white are in fathoms; those on shaded or dotted parts are expressed in feet (up to 18 feet). On general charts of the coast, curves indicating the range of soundings of 10, 20, 30, and 100 fathoms are shown. They are of great assistance when approaching a coast.

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On large general charts, for instance that of the North Atlantic Ocean, only the 100-fathom curve is given. soundings show the depth at mean low water.

67. Currents are indicated by an arrow, and the direction of the arrow shows the general direction of current; and the figures attached to them show the observed minimum and maximum rate of the current in nautical miles in 24 hours. On English charts the flood-tide stream is shown by an arrow, feathered on one side; ebb-tide stream by an unfeathered arrow, the velocity of the tide and stream being expressed in knots or nautical miles.

68. Buoys.-Channels on the coast of United States are indicated by red buoys, with even numbers situated on the starboard side when entering from the sea, and black buoys with odd numbers on the port side. Buoys with black and white perpendicular stripes are situated in the deepest part of the channel and should be passed close by.

Buoys with black and red horizontal stripes indicate danger, and obstructions with channels on either side of them.

69. Rocks just under water are indicated by a small dotted circle, with a cross in the center; rocks awash or just above water are indicated by dotted circumference with a small degree mark or black spot inside.

Rocks, islands, or shoals, with the letters E. D. close by,

signify existence doubtful; similarly the letters P. D. signify position doubtful, though known to exist. A wreck or dere

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71. Lights.-Lighthouses are indicated by a dot, colored yellow with a red spot or dash in the middle. Light vessels are indicated similarly with the image of a

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boat below the dot or dots, thus visibility of lights is given for an elevation of 15 feet above the surface of the sea.

72. Compass.-If the north and south line of a compass diagram is not on, or parallel with, a meridian, it is magnetic, according to the variation in the locality; if the line coincides with meridian it is true. The variation lines are indicated by a dash roulette, 35 dashes to the inch. The line of no variation is indicated by a dash roulette, 35 dashes to the inch, with a parallel full line underneath.

73. Meridian Used on Foreign Charts.-On English, Dutch, Scandinavian, Russian, Austrian, and American charts, Greenwich meridian is used as the first, or prime, meridian. On French charts the meridian passing through Paris is used; its longitude is 2° 20′ 15′′ or Oh 9m 21s east of the Greenwich meridian. The meridian of San Fernando, used on Spanish charts, is in longitude 6° 12' 24" or Oh 24m 49.6$ west of the Greenwich meridian. On Portuguese charts the meridian passing through the Marine Observatory, Lisbon, is used. Its longitude is 9° 11' 10" or 0h 36m 44.7 west of Greenwich. The meridian of Pulkowa Observatory, St. Petersburg, which is sometimes used on Russian

charts, lies in longitude 30° 19' 40" or 2h 1m 18.7s east of Greenwich. The observatory of Naples, the meridian of which is sometimes used on Italian charts, is in longitude 14° 15′ 7.3" or Oh 57m 0.5s east of Greenwich.

74. Soundings on Foreign Charts.-In order to facilitate the reduction of measurements of depth given on foreign charts into English measure, the following may prove useful.

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Russian, equal to English feet and fathoms.

The Spanish, Portuguese, and Italian Metro; the Dutch Elle and French Metre are identical.

75.

Abbreviations and Signs on English Charts. The abbreviations, signs, and symbols used on English charts are very nearly the same as on the American charts. The following tables of these abbreviations may be of value to the student.

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A number with a line above signifies no bottom at the depth given, thus 520 means that no bottom was reached with a lead line 520 fathoms long.

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