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HORIZON
1. The circle which bounds that part of the earth's surface visible to a spectator from a given point; the apparentjunction of the land and heaven. "And when the morning sun shall raisehismachine Above the border of this horizon." (Shak) "All the horizonround Invested with bright rays." (Milton)
2. The unbroken lineseparatingheaven and water, as seen by an eye at a given elevation, no earthbeing visible.
3. The epoch or time during which a deposit was made. "The strata all over the land, which were formed at the same time, are said to belong to the samegeological horizon." (Le Conte)
4. The chief horizontalline in a picture of any sort, which determines in the picture the height of the eye of the spectator; in an extended landscape, the representation of the naturalhorizon corresponds with this line. Apparent horizon. See Apparent. Artificial horizon, a level mirror, as the surface of mercury in a shallow vessel, or a planereflector adjusted to the true level artificially; used chiefly with the sextant for observing the doublealtitude of a celestial body. Celestial horizon.
See def. 2, above. Visible horizon. See definitions 1 and 2, above.
Origin: F, fr. L. Horizon, fr. Gr. (sc) the bounding line, horizon, fr. To bound, fr. Boundary, limit.
Source: Websters Vocabulary