ZENITH. The pole of the horizon, or that point in the heavens directly
overhead, as nadir is that which is directly under our feet.
ZENITH-DISTANCE. The angular distance of any celestial object from the
zenith at the time of observation. In navigation the meridional
zenith-distance of a heavenly body is much used for finding the
latitude.
ZEPHYR. The west wind, but generally considered to apply to any light
pleasant breeze.
ZERO. The cypher or nought at the beginning of a graduated arc.
ZETETIC. The analytic method of investigating a mathematical problem.
ZIG-ZAG. The winding trench of approach of a besieger, directed by short
turns alternately right and left of the defences of the place, to avoid
being enfiladed by them. Called also a _boyau_.
ZIG-ZAG COURSE. Working to windward by very short tacks or angular
turning boards.
ZODIAC. A broad zone or belt of the heavens, the middle of which is the
ecliptic, extending 9 deg. on either side of it. It is divided into twelve
signs, each measuring 30 deg. along the ecliptic.
ZODIACAL LIGHT. A pyramidal cone of light, apparently emanating from the
rising and setting sun, commonly seen in the tropics; in higher
latitudes most visible about the time of the equinoxes.
ZOLL, OR SAUL. An Indian timber, much used in the construction of
country vessels.
ZONE. _See_ BELT.
ZONE OF DECLINATION. A belt of the heavens included between certain
parallels of declination.
ZONES, IN GEOGRAPHY, are longitudinal belts into which the surface of
the earth is divided, according to their various relation to the sun's
apparent motion. They are--the _torrid_ or _equatorial zone_, bounded by
the two _tropics_ (which see), to every part of which, at some time or
other, the sun is vertical; the _frigid zones_, from the poles to the
polar circles, to every part of which in succession, periodically, the
sun is at mid-day below the horizon; and the _temperate zones_,
intermediate between the two former, to all of which the sun rises every
day in the year.
ZOOPHYTE. A term compounded of two Greek words, signifying animal-plant,
vaguely applied to various low forms of animal organizations, as the
sea-anemones and coral animals, which present a certain superficial
resemblance to plants.
ZOPISSA. Tar or pitch scraped off the bottoms of old ships, and thought
to be astringent and good for ulcers. Also, a highly preservative
varnish in use by the ancients for ships' bottoms, sarcophagi, &c.
ZUHN. A species of Indian rush, from which an inferior kind of cordage
and canvas is made.
ZUMBRA. A Spanish skiff or yawl.