Page:The American Cyclopædia (1879) Volume XIII.djvu/672

 652 POLAR CIRCLES Zaleski, and Padura; Odyniec, author of the drama of Izora ; Korsak, who wrote elegiac poetry and lyrics; Alexander Chodzko, trans- lator of Persian and other oriental poetry; Gorecki, Siemienski, Garczynski, Bielowski, Julius Slowacki, Groza, Krasinski, Zaleski, and numerous others. Novels were published in the earlier part of this century by Niemcewicz, Maria Czartoryska, Bernatowicz, and Skarbek, and more recently by Grabowski, Czajkow- ski, Zielinski, Kaczkowski, and especially Kra- szewski. Dramas have been written by Skar- bek, Kaminski, Fredro, Magnuszewski, Korze- niowski, and others ; the best historical works by Bandtke, Lelewel, Maciejowski, Narbutt, Eduard Raczynski, Plater, Szajnocha, and Lukaszewicz; the most popular educational works by Clementina Tanska- Hoffmann ; and philosophical works by Sniadecki, Trentowski, and Libelt. The most important works on Polish literature are by Mochnacki, Muczkow- ski, Bentkowski, Ossolinski, Chodynicki, Wisz- niewski (Historya literatury polslciej, 7 vols., Cracow, 1840-'46), and Lukaszewicz (Posen, 1860). The centres of Polish literary activity, and especially of periodical literature, are War- saw, Wilna, Posen, Cracow, Lemberg, and Paris, the latter city as the principal seat of the Polish emigration. Warsaw, however, in spite of very severe restrictions on the press, has always maintained a decided preeminence over all its rivals, as the literary metropolis of Poland. POLAR CIRCLES, two small circles or paral- lels of latitude, situated so that the arc of a meridian included between each of them and the nearest pole of the earth measures the an- gle of inclination of the earth's axis to the ecliptic. This angle is about 23 28', and the polar circles are therefore in about 66 32' N. and S. latitude respectively. The northern is called the Arctic, the southern the Antarctic circle. According to the common division of geographers, the former is the boundary be- tween the north frigid and the north temper- ate, the latter between the south frigid and the south temperate zones. They are also gener- ally considered as the respective boundaries of the Arctic and Antarctic oceans. The portions of the ear^h enclosed by the polar circles are the only regions in which the day or the night is ever more than 24 hours long. On the cir- cles themselves the greatest length of day (or of night in its alternation) is almost exactly 24 hours, and the length increases as the poles are approached until the six-months day or night of the pole itself is reached. The regions within the Arctic circle have been in some de- gree explored (see ARCTIC DISCOVERY, and PO- LAR SEAS), while those within the Antarctic circle are almost unknown. (See ANTARCTIC DISCOVERY.) POLAR CLOCK, an instrument invented by Sir Charles Wheatstone for showing the time of day by means of the polarized light of the sky. By referring to the subject of polariza- POLAR CLOCK tion in the article LIGHT, it will be seen that if a beam of light is passed through a polari- scope, and a plate of selenite or other double- refracting crystal is interposed between the polarizer and the analyzer to produce inter- ference and colorization, and the analyzer is rotated, the color will change into every grade of tint and pass into the complementary color. The effects will be the same whether the light is polarized by one piece of apparatus, or by re- flection from various objects lying in the direc- tion of the axis of the analyzer. As the light of the sky is polarized in a direction at right angles to the rays of the sun, it follows that if a Nicol's prism, serving as an analyzer, is placed with its axis parallel to the earth's axis and revolved so as to change its position with respect to the plane of polarization, the phe- nomena of change of intensity of light and color will be produced, as it also will if the apparatus is stationary while the sun revolves about it. The polar clock, constructed upon this principle, is described as follows by the inventor: u At the ex- tremity of a vertical pillar is fixed, within a brass ring, a glass disk, so inclined that its plane is perpendic- ular to the polar axis of the earth. On the lower half of this disk is a graduated semi- circle divided into 12 parts, and against the divisions the hours of the day are marked, commencing and ter- minating with VI. Within the fixed brass ring containing the glass dial plate, the broad end of a coni- cal tube is so fitted that it freely moves around its own axis ; this broad end is closed by an- other glass disk, in the centre of which is a small star or other figure formed of thin films of selenite, exhibiting, when examined with polarized light, strongly contrasted colors ; and a hand is pointed in such a position as to be a prolongation of one of the principal sections of the crystalline films. At the smaller end of the conical tube a Nicol's prism is fixed so that either of its diagonals shall be 45 from the principal section of the selenite films. The instrument being so fixed that the axis of the conical tube shall coincide with the polar axis of the earth, and the eye of the observer be- ing placed to the Nicol's prism, it will be re- marked that the selenite star will in general be richly colored ; but as the tube is turned on its axis the colors will vary in intensity, and in two positions will entirely disappear. In one of these positions a smaller circular disk in the centre of the star will be of a certain color, while in the other position it will exhibit the com- Polar Clock.