oxide of iron, protoxide of manganese, alumina, and water: sp. gr. 3.99. Y-level, in surveying, an instrument for measuring altitude and distance. Yttrium, a peculiar metal, discovered in the state of an oxide in Sweden; when heated to redness in the air, it takes fire, burns with splendour, and is converted into yttria.

Yttroce'rite, a mineral which occurs

Zaffre, in chemistry, the residuum or impure oxide of cobalt, after sulphur, arsenic, and other volatile matters have been expelled by calcination. Zamite, in geology, a fossil Zamia, which is a kind of Palm.

Zamtite (Sp.), a hydrous carbonate of nickel of an emerald-green colour. Zaph'ara, in the arts, a mineral used by potters to make a sky colour. Zar'athan, in pathology, a hard tumour of the breast, resembling a cancer. Zarnich, a genus of fossils that burns with a whitish flame.

Zea (Gr. zoo to live), a genus of important Grasses, Indian Corn or Maize, extensively cultivated in warm countries as an article of food.

Zebra Wood, a beautiful cabinet wood obtained from Demerara. Zechstein (Germ.), in mineralogy, a magnesian limestone lying under the red sandstone.

Zenith (Ital. zenit), in natural philosophy and ouranology, that point in the visible celestial hemisphere which is vertical to the spectator; the point directly overhead, and opposite to the nadir.-Zenith distance is the distance of a star or planet from the zenith, measured on the vertical circle passing through the zenith.Zenith sector is an astronomical instrument for measuring, with great accuracy, the distances from the zenith of stars which pass near that point.

Zeolite (Gr. zeo to foam, and lithos a stone), in mineralogy, a family of minerals, consisting of silica, alumina, lime, and water; natrolite.

Zero (Ital.), in meteorology, the point at which the graduation of the thermometer commences. The zero of Réaumur's and of the Centigrade thermometers is the freezing-point of water; that of Fahrenheit's thermometer, 32° below the freezing-point.

Zetetics (Gr. zeteo to inquire), a part of algebra which consists in the direct search after unknown quantities.

Zeuxite (Gr.), a greenish-brown mineral,

consisting of silica, alumina, protoxide of iron, lime, and water: sp. gr. 3.0; H = 4.25.

Zigzag (Fr.), an ornament in Gothic architecture; another name for the chevron.

Zigzags, in fortification, trenches or paths with several indented windings, so cut that the besieger cannot be enfiladed in his approaches. Zi'mome (Gr. zyme ferment), in chemistry, that part of the gluten of wheat which is insoluble in alcohol. Zinc (Germ.), a metal of a bluish-white colour, brittle when cold, but malleable when heated; much used in the manufacture of brass and other alloys. It is found in solid masses, sometimes in six-sided prisms, having the ends terminated in pentagons.Sulphate of zinc is found efflorescent in the form of stalactites, or in rhombs. Sulphuret of zinc is the most abundant of the zinc ores.Flowers of zinc, the oxide of zinc which flies up on the exposure of the metal to a temperature in the air very little above the melting-point, in the form of white flowers.-Zincamyl, colourless transparent liquid, composed of amyl and zinc. Zinc-bloom, an opaque mineral of a greyish dull lustre, composed of carbonic acid, oxide of zinc, and water. Zinc-ethyl, a colourless, transparent, and poisonous liquid, consisting of ethyl and zinc.-Zincomethyl, a volatile liquid of a very fetid smell, and consisting of carbon, hydrogen, and zinc. - Zinc-white, the oxide of zinc, used as a pigment for the same purposes as white-lead. Zincog'raphy (Germ. zink, and Gr.grapho to write), the art of drawing upon, and printing from, plates of zinc. Zingibera'ceæ, a nat. order of aromatic endogenous plants, of which Zingiber is the type. Zin'kenite, a crystallized mineral containing antimony, sulphur, lead, and copper: sp. gr. 5.30; H=3-3.5. Zircon, mineral composed chiefly of zirconia and silica, found in Ceylon.

a

a

Zoantho'ria (Gr. zoon an animal, and anthos a flower), in botany and zoology, a class of Zoophytes; animal flowers.

Zoan'thropy (Gr. zoon, and anthropos a man), in pathology, a species of monomania, in which the patient believes himself transformed into one of the lower animals.

Zoarchidæ (Gr. zoarchos a guiding animal), a family of the acanthopterygious fishes, of which Zoarchus is the type and genus.

Zodiac (Gr. zodiakos, from zoon an animal), in astronomy, an imaginary zone or belt in the heavens, extending about 8° or 9o on each side of the ecliptic. It is divided into twelve equal parts, called signs. -Zodiacal light is a faint nebulous brightness which accompanies the sun immediately before sunrise or after sunset.

Zoia'tria (Gr. zoon, and iatria medical treatment), in pathology, the treatment of the diseases of the lower animals.

Zo'isite (so called from Baron von Zois), a grey crystalline mineral, consisting of silica, alumina, lime, and protoxide of iron sp. gr. 3'32; Η = 6.25.

Zone (Lat. and Gr. zona), in geology, a division of the earth's surface by means of parallel lines. The zones are five in number, viz., the torrid zone, two temperate zones, and two frigid zones.

Zoo- (Gr. zoon), in natural history, a prefix to compound words relating to animals or animal life.

Zoochemical (Gr.), pertaining to the chemistry of animal organization. Zooch'omy (Gr.), that science which pertains to animal chemistry. Zoog'emy (Gr.), the doctrine of animal formation.

Zoog'raphy (Gr.), in natural history, a description of animals. Zooid (Gr. zoon), resembling an animal. Zo'olite (Gr. zoon, and lithos a stone), in geology, the fossil remains of a petrified animal.

Zoolithology (Gr.), a treatise on fossil animal remains.

Zoology (Gr. zoon, and logos discourse), in natural history, the science of animals, teaching their nature, properties, classification, &c. Zoon'omy (Gr. zoon, and nomos a law), in natural history, a treatise on the laws of animal life; the structure and functions of animals.

Zoopathology (Gr. zoon, pathos disease, and logos a discourse), a treatise on the diseases of animals.

Zoophagous (Gr. zoon, and phago to eat), eating animals; carnivorous. Zo'ophyte (Gr. zoon, and phyton a plant), a name applied to an order of Vermes, comprehending those beings supposed to partake of the nature both of vegetables and animals. Zo'ospore (Gr.), in zoology, a moving spore, provided with cilia or vibratile

organs.

Zoot'omy (Gr. zoon, and tome an incision), that branch of anatomy which relates to the structure of the lower animals; dissection of the bodies of animals.

Zoster (Gr. a girdle), in pathology, a cutaneous disease, commonly known as the Shingles.

Zurlite, the name of a recently-discovered Vesuvian mineral.

Zygoma (Gr.), in anatomy, a bone of the upper jaw; the process of the cheek bone.

Zygophylla'ceæ (Gr. zygon a yoke, and phyllon a leaf), in botany, a nat. order of Exogens, consisting of herbaceous plants, shrubs, or trees, of which Zygophyllum is the type.

Zymic (Gr. zyme fermentation), in chemistry, an epithet denoting an acid procured from a fermented substance, as leaven.

Zymology (Gr.), the doctrine of fer

mentation.

Zymom'eter, Zymosim'eter (Gr. zyme, and metron a measure), an instrument for measuring the degree of fermentation.

Zymo'sis (Gr. zymoo to ferment), in pathology, an epidemic or contagious affection, including fever, small-pox, cholera, &c.-Zymotic is an epithet pertaining to zymosis, or to an epidemic or contagious fever.