וויזיויו SE COMPASS CARDS. BOAT COMPASS. 12 13 14 15 16 17 18 19 20 21 22 23 24 2 3 4 5 NE + S זיויויויויו MS ווייוייי SE SHIP COMPASS. S 120 130 140 150 160 170 180 190 200 210 220 230 240 210 220 230 240 250 260 270 280 290 300 310 320 330's 10 20 30 40 50 60 CHAPTER VIII. THE COMPASS, LOG AND LEAD-SUBMARINE SIGNALS. § I. THE MAGNETIC COMPASS. The essential part of the compass is a magnetic needle which turns freely on a pivot, and which, if unaffected by local disturbing influences, would point due north and south (magnetic). The local influences which necessarily exist on ship-board and which on steel ships are very large, are more or less fully neutralized by the methods used to compensate" the compass; and the needle does, in general, point approximately to the magnetic poles. 66 A recent experience in which a ship was stranded because a small piece of iron had been carelessly left near the compass suggests the necessity for a warning on this point. Iron or steel, even in masses as small as a pocketknife, if brought near the compass, may affect it. Helmsmen and quartermasters should understand this. Stanchions, railings and other metal fittings near a compass should preferably be of bronze or other non-magnetic substance. If made of iron, they should never be absent, while the compass is in use, from the positions occupied when observations for deviation are made. Attached to the needle and moving with it, is a circular card marked around its circumference with two graduations; one of points, half-points and quarter-points, the other of degrees. (Plate 47 and 48.) The card with the attached needle (or needles) is floated in a liquid composed of 45 per cent pure alcohol, and 55 per cent distilled water, within a chamber, where it is pivoted upon a jewelled bearing which keeps the card centered and supports a small fraction of its weight. On the inside rim of the card-chamber is a vertical mark known as the "lubber's point," which, in installing the compass, is carefully adjusted in the fore-and-aft line of the ship with reference to the center of the card. In steering, this mark is held in coincidence with the point of the card indicating the course to be steered. The lubber's point is the thing that moves. The card is stationary. The graduation of the card in points and half-points runs as follows, beginning at North: NOTE. For convenience the 4 points between the 1⁄2 points are omitted in the above. They appear on the compass-card and are always given in Boxing the Compass; i.e., in enumerating the points and fractional parts of points from North around by way of East, South and West, back to North. North, South, East and West are called "Cardinal Points"; Northeast, Southeast, Southwest and Northwest, "Intercardinal Points." |