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POLAR CIRCLES

tition, 1795, put an end to the political existence of Poland. The subsequent wars of the French with the enemies of Poland caused the Poles to support Napoleon, but all that he accomplished was the formation of the duchy of Warsaw, 1807. By the Congress of Vienna, 1815, Austria's share of Poland was diminished, and Prussia received less than it had after the second partition. The greater part of the duchy of Warsaw was united, as the Kingdom of Poland, to the Russian Empire, but only by the bond of a common monarch. Thus finally Russia obtained 220,500 sq. m. Although Alexander I granted the so-called Kingdom of Poland a constitution, with a responsible ministry and a separate army, an insurrection occurred, 1830, which caused Rus

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sia to declare Poland an integral part of her empire. Uprisings took place 1846 and 1863; and, 1864, Poland was deprived of its last remnant of independ

ence.

Po'lar Cir'cles. ANTARCTIC; ARCTIC.

See

Polar Clock, instrument invented by Wheatstone, which, when accurately adjusted, indicates the apparent solar time within a very few minutes; operates even when the sky is overcast with clouds, provided there be an unobscured spot at the pole through which the blue sky may be seen. It applies the fact that the plane of polarization of sky light is always 90° from the sun.

POLAR CLOCK.

Polar Explora'tions. See POLAR RESEARCH. Polariza'tion, in optics, certain modifications in the character of the wave motions to which light is due. These modifications arise under certain conditions from reflection, refraction, etc. They are the source of some of the most beautiful and interesting phenomena. A beam of light from a self-luminous source, when passing through a homogeneous medium, exhibits the same properties on all sides so long as it does not meet with an obstacle; such a beam is composed of ordinary or natural light. But after it has been reflected or refracted, it has lost some of its properties; some of its rays have been quenched. When the reflection takes place at a certain angle, nearly all the rays except those lying in a certain plane will have been obliterated. If the ray, having been thus reflected from a glass mirror, be received obliquely on another glass mirror, and the latter turned around the ray, care being taken not to change the angle of incidence, the intensity of the twicereflected beam will vary as the position of the mirror is changed. If the second mirror is so placed that its plane of reflection is parallel to the plane of reflection from the first sur

POLARIZATION

face, the ray will be reflected without being diminished. But if the second mirror has its plane of reflection perpendicular to that of the first, the ray will not be reflected, or its intensity will be greatly reduced. When a ray of light from a luminous source falls on a glass plate at the polarizing angle, that portion of it which is refracted is also partially polarized. If that which has passed through one plate is afterwards transmitted through several in succession having their surfaces parallel, the polarization may be made tolerably complete. The planes of polarization of the reflected and the refracted rays are at right angles to each other, as are the planes of polarization of the ordinary and extraordinary rays in B Iceland spar.

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FIG. 1.

If two plates of crystal tourmaline, which has been cut in sections parallel to its axis, are laid at right angles on each other, as in Fig. 2, the combination will be opaque; if placed diagonally, as in Fig. 3, the opacity will be partial; and if they are placed parallel to each other, as in Fig. 4, the light will pass through both as if they formed one piece. The light in passing through the first plate of tourmaline has been polarized, its vibrations having been reduced to one plane. Therefore, in order that all the rays which have passed through the first plate may pass through the second, the axes of the two must be parallel.

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Various pieces of apparatus are used for investigating the properties of polarized light, but they always consist of two principal parts, a polarizer and an analyzer. In the case of the tourmaline plates, Figs. 2, 3, and 4, that through which the light first passes is the polarizer, and the other the analyzer. The reflecting polariscope is frequently given the form shown in Fig. 1, an arrangement in which the lower mirror is a plate of clear unsilvered glass. Rays of light reaching the mirror from the direction of a are polarized by reflection, and thrown downward upon the mirror c, whence they are returned vertically upward

POLAR REGIONS

through A B to the analyzer S, which is a mirror of black glass. The analyzer revolves within a graduated circle by means of which its position can be determined. An adjustable platform between the two mirrors supports objects the behavior of which when subjected to polarized light is to be studied.

Poʻlar Re'gions, regions situated near the N. and S. poles. The chief results of exploration in those quarters of the globe are the following: Each terrestrial pole is covered by a cap of continuous ice, which remains unbroken on the land areas and apparently over the smaller inclosed water areas of extreme high latitudes, and these caps vary in size with the season and with the year. Greenland is covered with an unbroken ice sheet, and so probably is also the S. continent. Around the margin of these caps is an area of variable width covered with floating ice, either derived from the frozen surface of the ocean when it forms the pack, the ice fields or the floebergs, or derived from the sheet of land ice when it forms icebergs. This area is more or less open, and at its outer margin is very open, irregular, and variable. Floating ice extends farther toward the equator in the Atlantic than elsewhere. In the N. Atlantic it may float as far S. as lat. 42° N. and in the S. Atlantic to lat. 39° S. In general the surface currents of the ocean flow away from the ice caps. An exception is found in the Antarctic field, where S. of New Zealand a current sets in toward the great bay in this field. Another is in the Arctic field, where the Gulf Stream extended enters the Arctic to the N. of Scandinavia.

The entire Arctic area (extending far S. in Siberia and N. America) has a mean annual temperature of 32° or lower, except the NE. coast of Norway and a coastal strip of small size on E. Greenland. The seasons are reduced to two, summer and winter, and the diurnal changes are relatively slight. The greatest cold in winter is in the Yana basin, where the mean temperature for January descends to -50° F. or lower. The July mean temperatures run from 36° F. in the vicinity of the pole to about 50° F. near the Arctic circle. The precipitation about the pole is small, varying from 8 to 25 in., and is somewhat more likely to fall in late summer than at other seasons. The accumulations of ice and snow are due to the conservation of what has fallen. It is largely in the form of snow, and evaporation is small because of the low temperatures. Fog and high winds are common. The N. magnetic pole was found by Ross to be on Boothia Felix in 1831. It has since traveled a few degrees E. and is now near the SE. angle of this peninsula, at about lon. 70° 5' N., lat. 96° 44' W. The S. magnetic pole was found by a party under the direction of Lieut. (now Sir) Ernest H. Shackleton in 1909, in a hitherto unexplored area S. of Australia and in lat. 72° 25', lon. 15° 4' E. Arctic researches have given opportunity for many studies of the aurora. The center of greatest frequency

is in NE. America.

The geology of the Arctic region is diversified. Certain Cretaceous and Tertiary strata

POLAR RESEARCH

in Spitzbergen, N. Greenland, and the Arctic Archipelago show that in Cretaceous times this area had a subtropical climate with a luxuriant flora, something like that now found in S. Japan. Fossils obtained in the Antarctic region show that this also had at one time a warm climate. Volcanic action is seen

only about the S. pole. The flora of Arctic regions is scanty. Willows, dwarf birches, and a few other shrubs extend to S. Greenland, and a dwarf willow extends far N. The flowering herbs of high latitudes are few. Beyond these are found only mosses, algæ, and lichens. The Antarctic flora is more scanty than the Arctic. In the Arctic regions animal life is relatively abundant. N. of lat. 81° are found the Arctic bear, the wolf, two species of fox, the reindeer, musk ox, etc.; also three species of seal, two of whale, the swordfish, and the narwhal. Thirty-two species of birds have been observed N. of 81° 31′ N., and the most of these have also been seen at Point Barrow and on Nova Zembla and Spitzbergen. The rock ptarmigan is the only winter resident. There are also many fish and lower marine forms and insects. The Antarctic region has generally been represented as swarming with the marine forms of animal life. Here have been found five species of whale, four of seal, and twenty of birds, penguins being numerous.

The Antarctic area is uninhabited by man, as also are Nova Zembla, the New Siberian Islands, Franz Josef Land, Spitzbergen, Jan Mayen, and the Arctic Archipelago, but on the coasts of the last named are many evidences of a former occupation by the Eskimo. The Lapps occupy the Arctic coasts of Europe W. of the White Sea, and the Samoyeds E. to the Yalmal Peninsula. From the Kolyma mouth to Bering straits the coast is occupied by the Chukchees, who also extend S. about the Anadyr Gulf. The Arctic coast of America, both sides of Baffin Bay, and Davis Strait, and the SE. coast of Greenland are occupied by Eskimos. The extreme N. of these are the Arctic Highlanders, who occupy the W. shore of Greenland to the N. of Melville Bay. They now reach in their migrations no higher N. than lat. 79°, but traces of their former occupation can be found farther N. and on Grinnell Land. See POLAR RESEARCH.

Polar Research', exploration of the regions about the poles of the earth. The older attempts were devoted to finding a NE. or NW. passage, or to reaching the geographic or magnetic poles. They were unsuccessful, except in finding the N. magnetic pole, and they did not add greatly to knowledge. Sir Hugh Willoughby, an English navigator, attempted, 1553, to find a route to China and India by the N. of Europe and Asia. Two of his ships reached Kalguev Island, but were never heard from afterwards. The third reached the mouth of the Dwina in safety, and the White Sea was opened to British commerce. Later, Stephen Burroughs reached Vaygach Island, and, 1580, Pet and Jackman penetrated the Kara Sea. Barents, a Hollander, reached Nova Zembla, 1594, discovered Spitzbergen, 1596, and reached a lat

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POLAR RESEARCH

POLAR RESEARCH

itude of at least 80° N. In the seventeenth | drée, a Swedish aëronaut, had attempted to century Franz Josef Land was apparently reach the pole by balloon from Spitzbergen, reached by a whaler named Roule. Attempts but has never returned. to penetrate farther E. than Nova Zembla and the Kara Sea were unsuccessful until 1878-79, when the passage was made by Nordenskjöld. Journeying from Spitzbergen, Hudson, 1607, discovered Jan Mayen. The sea to the N. being usually blocked by ice, expeditions were undertaken on sledges; the highest latitude reached in this way was 82° 45′ N. by Parry, 1827.

The greatest activity in Arctic exploration has been to the N. of the American continent in the Arctic Archipelago, and especially along the W. coast of Greenland. This coast was apparently visited by Nicolas and Antonio Zeno, Venetians, in the fourteenth century. It also offered the problem of the Northwest Passage, corresponding to that of the Northeast. Sebastian Cabot unsuccessfully searched for this passage, 1498, and was followed, 1576, by Frobisher. The search was actively continued by Davis, Hudson, Ross, Parry, Richardson, Franklin, and others. The geographic results of the search for Franklin were very rich, and the complicated and ice-covered Arctic Archipelago was explored.

Hayes was convinced that an open sea exists about the pole. He returned, 1860, and reached the lat. of 81° 35' N. by way of Smith Sound, but did not find the open sea. For the winter 1882-83, by international coöperation, stations were established within the Arctic and Antarctic circles, chiefly to carry on meteorological and magnetic observations. The extreme N. of these was that established, 1881, at Lady Franklin Bay, on the E. coast of Grinnell Land, in lat. 81° 44′ N., under the charge of Greely.

The search for the Northwest Passage was officially terminated in 1853 upon its discovery by Sir Robert McClure. Records recovered by McClintock in 1859, however, show that its discovery by a more southerly route was made by John Franklin in 1847. But neither of these explorers ever fully traversed the passage. This feat was first accomplished by Capt. Roald Amunsden, a Norwegian, who sailed from Christiania in June, 1903. stopped for investigations at the magnetic pole, but found no decided change from the magnetic conditions observed by Ross in 1831. Taking the more southerly passage discovered by Franklin, he completed his journey in August, 1906.

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Up to December, 1894, the extreme N. point reached by civilized man was on the N. coast of Greenland, in lat. 83° 24', gained by a party under Lieut. Lockwood. In 1893-96 Nansen penetrated to lat. 86° 175'. In 1894-97 Fred. G. Jackson discovered a number of islands and Victoria Sea N. of Franz Josef Land. During 1891-92 Peary determined the insularity of Greenland, and, 1898-1902, attained what was then highest N. in the W. Hemisphere (83° 39'). The Duke of the Abruzzi, 18991900, reached 86° 33′ N. Peary, 1906, reached 87° 6' N., by way of Smith Sound, traced the N. coast of Grant Land, and discovered new land in about 100° W. Meanwhile, 1897, An

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On July 6, 1908, the Roosevelt, equipped by the Peary Arctic Club and commanded by Peary, left New York on the trip which resulted in the discovery of the N. pole. The expedition wintered near Cape Sheridan. The sledge expedition left the Roosevelt in three divisions on February 15th, 21st, and 22d. They united later at Cape Columbia. The total of the three divisions comprised 7 white men, 59 Eskimos, 23 sledges, and 140 dogs. When they reached 84° N. lat. part of the party was sent back and 16 men, 12 sledges, and 100 dogs pushed forward on a quick march. On April 6th Peary, accompanied by a negro (Matt Henson) and 6 Eskimos, reached the pole. He found the pole, as has been supposed for many years, to be surrounded by a continuous ice field. He found a temperature of 33° below zero. The bottom of the sea at that point was not found by a sounding of 9,000 ft.

The lands of the Antarctic region were unknown and unsuspected until 1773-75, when they were discovered by Cook, who showed that the S. continent was isolated and almost entirely within the Antarctic circle. In 1819 an English whaler, William Smith, was driven S. of the Falkland Islands to S. Shetland. In the early part of the nineteenth century the Messrs. Enderby, of London, interested in whaling, instructed their captains to explore as far S. as possible. Their Capt. Briscoe, 1831, discovered Enderby Land, about one third of a circle E. from S. Shetland and forming the second angle of the triangular S. continent. In 1832 he discovered and landed on Adelaide Island. He was apparently the first man to set foot on the S. continent. In 1838 their Capt. Balleny discovered the third angle of this continent in what is now known as Wilkes Land. In 1839-43 the Antarctic region was visited by a U. S. expedition under Wilkes, a French one under d'Urville, and a British one under Ross. Ross penetrated to 78° S. in the latitude of New Zealand, and discovered the mountainous district of Victoria Land, terminating to the S. in the active volcano Mt. Erebus, 12,000 ft. high.

In 1895 Carsten E. Borchgrevink, of Norway, set foot on the mainland of S. Victoria Land; 1897, attempted to reach the S. Pole without success; and returning to London, 1900, reported having reached lat. 78.5° S., lon. 195.5° E A Belgian expedition under Lieut. De Gerlache passed the first winter ever spent by men in the Antarctic regions, 1898-99, and their vessel was frozen in the ice a full year, drifting with it between 70° and 71° 36′ S. lat. and 85° and 103° W. lon. Dr. Otto Nordenskjöld, of Sweden, headed an expedition, 1901-4, to Cape Seymour, about 800 m. SE. of Cape Horn, and there discovered fossils which indicated a previous warm climate. An English expedition under Capt. R. F. Scott, 1901-4, explored the inland ice of Victoria Land and reached 82° 17' S. In 1902-3 a German expedition under Prof. Von Deygalski discovered in lat. 66° 2′, lon. 89° 48′ E. a point

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