ZENITH SECTOR. 



ZINC. 



1048 



one of the bands is a little longer than the other, then a very large 

 angular motion of the band will give a small angular motion to the 

 telescope-bar, and as the measurement of the former angle can be 

 easily made with tolerable accuracy, the latter angle can be computed 

 with great exactness.* Exquisite workmanship would no doubt be 

 required to make such an instrument answer, but we think that for 

 this and other differential purposes Sir. Babbage's suggestion is de- 

 serving of attention, ; especially where telescopes of limited size are 

 used. 



The adjustments of a zenith sector or zenith tube will differ accord- 

 ing to the construction of the instrument. Where it is not reversible, 

 the time of the transit of a star near the zenith must be got from 

 observations with another instrument, and the star made to pass the 

 meridian-wire at the calculated time by the proper adjusting screws. 

 When this is done and the telescope secured, a star must be made to 

 pass along the declination-wire (this should be carried by a micrometer- 

 screw) by twisting the wire-cell, when the adjustment for a fixed zenith 

 telescope is complete. If the telescope rest on a cross axis and carries 

 a sector, the cross axis must be made horizontal, the transits of stars 

 towards the extremities of the arc must be observed, and the azimuthal 

 deviation ascertained [TBASSIT] and corrected; or, the time at which 

 an extreme star should pass being known, the cross axis at top and 

 fixed arc below must be turned so as to make the star pass at the right 

 time. 



When the instrument is reversible, the axis is first to be set truly 

 upright. Suppose the instrument in its meridian position nearly, and 

 face east, read off the division bisected by the plumb-line, or the two 

 ends of each leveL Now turn half round, read off again, and bring, by 

 the adjusting screws, the plumb-line or the levels half-way to the first 

 readings, and finally adjust each level by its own screw to read each 

 end alike. If this be carefully done, when the instrument is restored 

 first position, the plumb-line or levels will remain undisturbed 

 by the last reversal. Now turn the axis one-quarter round, and correct 

 whatever change is thereby caused, by the east and west screws of the 

 axis. The axis is now vertical, or by a repetition of the process may 

 be made so. The next adjustment is to make the line of sight describe 

 a great circle. This is the colh'mation error of the transit. This may be 

 done as described above, from knowing the true time ; or by observing 

 one star or two stars near the zenith in reversed positions, when the 

 disagreement between the observed and computed difference will give 

 the quantity and direction of the alteration required. In a modern 

 instrument this adjustment would be by antagonist screws carrying 

 the wire-plate. If the instrument be simply a zenith-tube, make a 

 star run along the declination-wire, and the adjustment is finished. 

 With a sector place the instrument nearly in the meridian, observe the 

 transit of a zenith star, which gives the time. Then by turning round 

 the axis, make an extreme star pass at the proper time and clamp the 

 axis. In the present ordnance sector the instrument rests on a tray 

 which \ adjusted as to meridian by strong screws on the stand, acting 

 against the sides of the tray. Finally, twist the wire-cell till a star 

 runs along the declination-wire. A comparison of the zenith distances 

 of the same stars observed in reversed positions of the instrument, will 

 give the error of collimation, and this may be corrected if the observer 

 wishes, but it is better to leave it untouched, and to consider the sum 

 of two observations, Face East and Face West, as a double zenith 

 distance. 



(For plates and descriptions of some of the constructions here 

 referred to, and others which we have omitted, see Pearson's Practical 

 Astronomy, vol. ii., pp. 631, 554, plates xii., xiii., xxvi., xxvii.) 



ZBNZO, ZENZIC. The AAbs used a word for the square of a 

 number which has the same meaning as the Latin word census ; 

 accordingly Leonard of Pisa, Lucas Pacioli, and the early Italians, used 

 radio and cota for the unknown quantity, and census for its square, 

 which became censo in Italian. The Germans corrupted these into 

 zenzus and zenzo, and hence in then- algebraic writings, and in some 

 of the early English ones, the zenzic power is the square. From this 

 and the word cube, various denominations of powers were formed, as 

 zcnzi-cubic for sixth, zenzizenzizenzic fur eighth, &c., from which we 

 are now happily delivered. 



ZERO. [THEBMOMETEn.] 

 ZERO. flNFIJilTK, &C.J 



ZETETICS, a name given by VIETA [Bjoa. Div.] to the part of 



Let the length of the upper band be a, of the lower band a + h, the dis- 

 tance between (he bands b, and let the bands be horizontal ; the telescope-bar 



A 

 make* with the zenith an angle the tangent of which = ; when the bands are 



h x cos 

 inclined at an angle 0, the tangent of zenith distance = r . The quantity 



A may be measured and regulated by a micrometer-screw and such a tilt given 

 to the telescope, that the star can be observed in reversed positions of the axis, 

 and thus the double zenith distance found. The zero of the micrometer-screw 

 it found from Its position, when openiug and closing the bars makes no change 

 in the place of a star. Wo prefer this construction of a zcniUi sector to 

 that of Mr. tiabbagc. The zenith point is only to be got by reversion, and the 

 upright bar must be watched and ascertained by levels, &c. Mr. Babbagc has 

 given an exact formula, when the points of attachment of the telescope-bar arc 

 fjnstant. We have supposed an adjustment in one of these points, which allows 

 the bands to be horizontal, while the telescope-bar is inclined. 



algebra which consists in the direct search after unknown quantities : 

 it is now disused. 



ZEUS, the supreme deity of the Greek Olympus, the god of heaven 

 and of earth, to whom the Jupiter of the Romans nearly corresponds 

 both in power and attributes, was probably originally an elemental 

 divinity, who was worshipped as the god of rain, snow, lightning, &c. 

 Apart from other considerations the etymology of his name, both in 

 Greek and Latin, would seem to lead to this conclusion. 



According to Homer, Zeus was the son of Kronos and Rhea. 

 [KKONOS.] In order to save her son from being destroyed by his 

 father, Rhea concealed him soon after his birth in a cave in Crete, 

 where he passed the first years of his life. As Zeus grew up, Kronos 

 called to his aid the Titans, in order to secure his dominions against 

 his son ; but they were eventually conquered, and Kronos himself 

 dethroned by the youthful Zeus. In the Homeric poems Zeus is 

 represented as the supreme ruler of the gods and of men ; and though 

 subject himself to the decrees of Fate, his commands cannot be dis- 

 obeyed ; his wisdom is infinite, and his power irresistible. His wife 

 was Hera, and their children Hephiestus, Ares, and Hebe. The wor- 

 ship of Zeus was co-extensive with the Grecian race. His temples 

 were numerous, the chief being at Elis and at Athens the former con- 

 tained Phidias's sublime chryselephantine statue of the god, the 

 latter being, when perfect, the noblest temple perhaps of the ancient 

 world. 



Cicer.0 informs us ('De Nat. Deor.,'iii. 21) that there were three 

 Roman deities of the name of Jupiter: one the son of JEther; the 

 second, the son of Heaven ; and the third, the son of Saturn. The 

 last was worshipped at Rome under various names, and many temples 

 were erected to his honour, of which the most celebrated was the one 

 on the Capitoline Hill, where he was worshipped under the name of 

 Jupiter Optimus Maximus. 



As the supreme god, Zeus taxed the highest powers of the artists of 

 ancient Greece. The Greeks themselves believed that Phidias, in the 

 seated chryselephantine statue of Zeus which he executed for the 

 temple of Elis, had attained the loftiest conception of the divinity. 

 Zeus himself, Pausanias tells us (b. v. o. 10), gave a visible expression 

 of his approval of the sculptor's art ; and Quinctilian declares that the 

 work equalled in majesty the god himself, and added somewhat to the 

 religion of those who saw it. The statue has long been lost, but 

 several attempts have been made to restore it from contemporary 

 descriptions the best known being that of M. Quatremere de Quincy, 

 in his 'Jupiter Olympine.' This work of Phidias seems to have been 

 accepted by the Greeks as an authoritative model for the form and 

 features of the deity. Phidias probably followed in the general 

 conception some more ancient type, but his was thenceforward the 

 normal form which all succeeding artists, according to their ability, 

 sought to reproduce. Miiller thus characterises the external features 

 of Zeus, as found in works of the best and later periods of Greek art : 

 " The hair rose up from the centre of the forehead, like that of a lion, 

 and then fell down on both sides like a mane ; the brow clear and 

 bright above, but greatly arching forward beneath; eyes deeply sunk, 

 but wide open and rounded ; delicate mild lineaments round the upper 

 lip and cheeks ; the full rich beard descending in large wavy tresses ; a 

 noble, ample, and open chest, as well as a powerful, but not unduly 

 enlarged muscular development of the whole body." (' Ancient Art, 1 

 349.) From this general character, which belongs to the best statues 

 of Zeus, deviations occur, where he is represented in a youthful form, 

 or as an excited and vengeful deity. 



Zeus was usually represented seated on an ivory throne, with a 

 sceptre in his left hand and in his right a thunderbolt. The Olympian 

 Zeus of Phidias bore in his right hand a Victory, made like the statue 

 itself, of gold and ivory. In early art the representations of Zeus 

 chiefly have reference to his divine character, and his more sublime 

 attributes. Later, and especially as art became the minister of luxury, 

 and too often of voluptuousness, the intrigues of the god with the 

 lesser goddesses, and with mortars, afforded a more acceptable class of 

 subjects, and Jupiter and lo, Jupiter and Ganymede, Leda and the 

 like, were figured in every variety of form and material ; and at the 

 revival of the study and imitation of classical art, it need hardly be 

 added that this series of circumstances in the mythic history of Jupiter 

 was seized upon with avidity by the painters and sculptors of Italy. 



ZIF. This name, written )t in Hebrew, occurs only in the first 



book of Kings, in the 6th chapter, and in the 1st and 37th verses. It 

 is the mouth now called Jyar. The word is derived by the Jews from 

 a root signifying to be splendid, in reference to the splendour of the 

 season when the month occurs, April and May. The word is found 

 several times with a slight orthographical difference in the book of 

 Daniel, and is usually translated " brightness." [BuL.] 



ZINC (Zu). Spelter. A commercial metal which has been known 

 in the metallic .state since the time of Paracelsus. It ia never met 

 with in the native state, but is extracted from two ores calamine, or 

 carbonate of nine, and blende, or sulphide of zinc. A native oxide of 

 zinc found in New Jersey has also recently been rendered available for 

 the extraction of the metal. 



The commercial metal is never pure, though usually sufficiently so 

 for most chemical purposes. The pure metal may be obtained by 

 dissolving common zinc in dilute sulphuric acid, filtering, treating 



