ZER 



ZI N 



ZE'CHSTEIN. A magnesian of lime- 

 stone, abounding in Germany, and be- 

 longing to the New Red Sandstone 

 group. 



ZE'IN. A substance procured from 

 the zea mays, resembling gluten, but said 

 to be destitute of nitrogen. 



ZENITH AND NADIR. These are 

 astronomical tenns derived from the 

 Arabic, and they denote two points of the 

 sphere of the heavens, the former verti- 

 cally over a spectator's head, the latter 

 vertically under his feet ; they are, there- 

 fore, the vanishing points of all lines 

 mathematically parallel to the direction 

 of a plumb-line at his station. They are 

 the poles of the celestial horizon, i. e. 

 points 90° distant from every point in it. 



ZENITH DISTANCE. An astrono- 

 mical term, denoting the complement of 

 the altitude of the sun, or other heavenly 

 body. Vertical circles of the sphere are 

 great circles passing through the zenith 

 and the nadir, or great circles perpen- 

 dicular to the horizon ; on these are 

 measured the altitudes of objects above 

 the horizon — the complements to which 

 are their zenith distances. 



ZENITH SECTOR. An astronomical 

 instrument, consisting of a portion of a 

 divided circle, employed for measuring 

 accurately the zenith distances of stars 

 which pass near the zenith. This instru- 

 ment is also used in trigonometrical sur- 

 veys for determining the difference of 

 latitude of two stations ; for the differ- 

 ence of the zenith distances of the same 

 star, observed at its meridional passages 

 at two places, gives the difference of the 

 astronomical latitudes of the places with- 

 out any reu'ard to the star's declination 

 *"*■ ZE'OLITES (t^o), to boil, XiOoi, a 

 stone). A term applied to the silicates 

 of lime and alumina, from their frothing, 

 when heated before the blow-pipe. This 

 is a very extensive mineral genus, con- 

 taining the dodecahedral species, or leu- 

 cite; the hexahedral, or analcime; the 

 rhomboidal, oxchabasite; the pyramidal, 

 or cross-stone; the diprismatic, or lau- 

 monite; the prismatic, or mesotype, com- 

 prising the fibrous zeolite, natrolite, and 

 mealy zeolite ; the prismatoidal, or stil- 

 bite, comprehending foliated and radiated 

 zeolite ; and the axifrangible, or apo- 

 phyllite. 



ZE'RO (tsnphara, Arab., empty). A 

 term used to denote a cipher placed be- 

 tween the ascending and the descending 

 numbers of a scale or series. The zero 

 of Fahrenheit's thermometer is 32° below 

 382 



the melting point of ice; that of the cen- 

 tigrade scale coincides with the freezing 

 point of water. The absolute zero is the 

 imaginary point in the scale of tempera- 

 ture at which the whole heat is ex- 

 hausted ; it is the expression of absolute 

 cold, or privation of caloric. 



ZERO POINT. The term applied by 

 astronomers to that point of the equi- 

 noctial, called the equinox, through which 

 they suppose the hour circle to pass, from 

 which all others are reckoned, and which 

 point is itself the zero point of all right 

 ascensions counted on the equinoctial. 



ZETE'TICS iCnreu), to search). The 

 name given by Vieta to the department 

 of algebra which consists in the direct 

 search after unknown quantities. The 

 term is now obsolete. 



ZEUXITE. A zeolitic substance, found 

 in Huel-Unity Mine, near Redruth, in 

 Cornwall. 



ZINC. A bluish-white metal, occur- 

 ring in the form of oxide, or red zinc; 

 of sulphuret, or blende; of carbonate, or 

 calamine; of sulphate, or white or zinc 

 vitriol; of silicate, or electric calamine; 

 and of aluminate, or automalite ox gahnite. 

 It has been called marcasite, Indian tin, 

 and spelter. When rolled into thin leaves, 

 it is termed sheet zinc. The mineral sub- 

 stance, zinc bloom, is of the same com- 

 position as calamine, or the carbonate of 

 this metal. 



1. Zinc, floivers of. This is the oxide, 

 formed by exposing the metal to the air 

 at a temperature a little above its melting 

 point, when it flies up in the form of 

 white flowers. It has hence received the 

 fanciful names of nihil album and philo- 

 sophical wool. By the ancients it was 

 called pompholix. In Holland it was 

 sold as a secret remedy under the 

 names of luna Jixata and arcanum Lude- 

 manni. 



2. Zinc, butter of. This is the chloride 

 or hydrochlorate, obtained as a whitish- 

 grey mass, with the consistency of wax 

 or butter. 



ZINCOID AND CHLOROID. These 

 terms are applied, on the electrical hypo- 

 thesis, to the plates of a decomposing 

 cell : the chlorous plate, which is in con- 

 nection with a zinc plate, is termed the 

 chloroid (like chlorine, quasi-chlorine), 

 and is the same as the negative pole, the 

 negative electrode, the cathode and the 

 platinode ; while the zincous plate, which 

 is connected with a copper plate, is called 

 the zincoid (like zinc, quasi-zinc), and 

 represents the positive pole, the positive 



