OBLIQUE BEARINGS. Consist in determining the position of a ship, by observing with a compass the bearings of two or more objects on the shore whose places are given on a chart, and drawing lines from those places, so as to make angles with their meridians equal to the observed bearings; the intersection of the line gives on the chart the position of the ship. This is sometimes called the method of cross-bearings.
OBLIQUE SAILING. Is the reduction of the position of the ship from the various courses made good, oblique to the meridian or parallel of latitude. If a vessel sails north or south, it is simply a distance on the meridian. If east or west, on the parallel, and refers to parallel sailing. If oblique, it is solved by middle latitude, or Mercator sailing.
OBLIQUE STEP. A movement in marching, in which the men, while advancing, gradually take ground to the right or left.
OBLIQUITY OF THE ECLIPTIC. The angle between the planes of the ecliptic and the equator, or the inclination of the earth's equator to the plane of her annual path, upon which the seasons depend: this amounts at present to about 23° 27′.
OBLONG SQUARE. A name improperly given to a parallelogram. (See [Three-square].)
OBSERVATION. In nautical astronomy, denotes the taking the sun, moon, or stars' altitude with a quadrant or sextant, in order thereby to find the latitude or time; also, the lunar distances.
OBSERVE, To. To take a bearing or a celestial observation.
OBSIDIONAL CROWN. The highest ancient Roman military honour; the decoration of the chief who raised a siege.
OBSTACLES. Chains, booms, abattis, snags, palisades, or anything placed to impede an enemy's progress. Unforeseen hindrances.
OBTURATOR. A cover or valve in steam machinery.