ZENITH TELESCOPE. 768 ZENO. one or more movable threads carried by a single micrometer screw with a graduated head reading to the required accuracy. The zenith telescope was invented by Captain Andrew Talcott, of the United States Engineers (1S34), to carry out practically the principle that when the meridian zenith distances of two stars (one north and the other south of zenith), at their upper culminations, are equal, the colat- itude is the mean of their north polar distances. This method of finding the latitude is known as Talcott's method. Since two stars having exactly the same meridional zenith distance can rarely be found, two having nearly the same are selected. Refraction is consequently almost elimi- nated. The telescope is first pointed to the star which first comes to the meridian, and the spirit level is set horizontal. As the star passes the field of view its distance north and south of the central horizontal wire is measured by the micrometer. The instrument is then revolved 180° and the second star observed in the same manner. In revolving the instrument care must be taken that the angle between the level and the telescope is not disturbed. The latitude is then given bv the formula where d^ and 5^ are the declinations of the two stars; and f, — f„, the difi'erence of their zenith distances, determined by the micrometer meas- urement. Consult Chauvenet, Spherical and I'laiiical Astronomi/ {Philadelphia, 1803). ZENJAN, zen-jiin'. A town of Persia. See ZixjAX. ZENKEK, tseu'ker, Friedrich Albert von (1825-98). A German physician, celebrated for his discovery of trichiniasis. He was born in Dresden, and was educated in Leipzig and Heidelberg. Attached to the city hospital of Dresden in 1851, he added, in 1855, the duties of professor of pathological anatomy and gen- eral pathology in the surgico-medical academy of that citv. In 1862 he became professor of pathological anatomy and pharmacology at Er- langen. Three years afterwards he assumed with Zicmssen the editorship of the Deutsches Archiv fiir llinische iledizin. In 1805 he re- tired from active service. His important discov- ery of the danger of trichinae dates from 18G0. In that year he published Veber die Trichinen- Icrankheit des Menschen (in vol. xviii. of Vir- chow's Archiv). This was followed by Beitriicje zur normalen und pathologischen Anatomie der h-unge (1802); Veber Staubinhalation.tkrank- heiten der Lnngen (1860) ; Die Krankheiten des Oesophagus (in vol. vii. of Ziemssen's Handbiich der spe::ieUen Pathologic und Therapie, 1877). ZE'NO (Lat., from Gk. Zijvwv, Zenon) (e.488 li.c.-?). An Eleatic philosopher, born at Elea ( Velia) . a town of T.iicania in Southern Italy. He was a favorite pu])il of I'armcnidos. At the age of forty he accompanied his master (o .thens, where he resided some time and numbered among his pupils Pericles and Callias. Tradition says that after his return to Elea he joined a move- ment to deliver the city from the tyrant Near- chus, and when the attempt failed, he was cap- tured and put to torture. Of this, however, the evidence is not satisfactory. As a folhnvcr of Parmenides lie snp])orted his doctrines by in- direct demonstration, in which he attempted to point out that belief in the real existence of changing phenomena led to contradiction. He tried to establish the truth of the unit}' of being by showing that the hypotheses of motion, mul- tiplicity, and sense have inherent contradictions. To the real existence of motion he objected that motion cannot begin, because the moving body cannot arrive at any place from that in which it is until it has passed through the unlimited number of intermediate spaces. Now, as it is at any given moment in a particular place, it can- not leave that position, therefore the fiying arrow is in reality at rest. His second argument was the famous proof that Achilles cannot overtake the tortoise because at any moment he only reaches the place previously left by the tortoise; his other arguments are similar. He likewise argued against the reality of space, for, if all that exists were in a given space, that space itself would be included in another space, and so on without limit. Against sense perception he said that if a measure of grain in falling pro- duced a sound, every single grain and smallest fraction thereof must produce a sound; but if the latter be not true, then the whole measure, whose efl'ect can be nothing but the sum of the effects produced by its parts, can produce no sound. Zeno's arguments against the reality of motion were answered by Aristotle in his Physics, but the argument still had considerable influence on the development of metaphysics in the latter period. Consult: Ritter and Prcller. Historia Philosophiw Grwcw (Sth ed., Gotha, 181)8) ; Zel- ler. Philosophic der Griechen (4th ed., vol. i., Leipzig, 1900) ; also, Zeller's Pre-Socratic Phi- losoplig, vol. i. (New York, 1881); I'cberwcg, History of Philosophy, vol. i. (New York, 1887). ZENO (4th and early 3d century B.C.). The founder of Stoic philosophy, born at Citium. in the island of Cyprus. The exact date of his birth is unknown, as is that of his death. b>it he is said to have lived to a great age. He was the son of a merchant, and was himself eng.agcd in trade during the earlier part of his life, but according to tradition a shipwreck caused him to reside for a time at Athens, where the works written by the disciples of Socrates in regard to their master filled him with admiration, and he joined himself as pupil to Crates the Cynic. His earliest writings according to tradition contained mucli that savored of the harshness and blunt- ness of the Cynic doctrine. Failing to find suffi- cient satisfaction from Cynic philosophy, he turned to the Megarian Stilpo, from whom he learned the art of disputation, and later to Xenocrates and Polemo of the .Academy. Not long after n.r. 310 he founded his own school in the Painted Piu-cli (UoikIXtj Iroi'i] . where, accord- ing to Apollnnius, lie (auglit for fifty-eight j'ears. Diogenes Lacrlius mentions a number of works by liim, no one of which has been )n"cscrvcd. He and his followers strove to realize the virtuous wise man for whom the iilealized Socrates was a model. The ethics of the school, which were strongly influenced by Cynicism, were most pro- ductive in that they discriminated carefully be- tween what was simply right and good and what was agreeable. Their physics were strongly in- (hieneed by Pythagoras and Heraclitus. The .Allu'nians held ZcTm in great regard during his life, and after liis death honori'd him with a
