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Rh PLANCK, KARL CHRISTIAN (1819–1880), German philosopher, was born at Stuttgart on the 17th of January 1819. He studied at Tübingen, where he became doctor of philosophy in 1840 and Privatdozent in 1848. During this period the influence of Reiff led him to oppose the dominant Hegelianism of the time. In 1850–1851 he published his great book, Die Weltalter, in which he developed a complete original system of philosophy, based on the realistic view that thought should proceed from nature to the highest forms of existence in the spiritual life. Not only did Planck oppose the idealism of his confreres, his views were, in another aspect, directly antagonistic to the Darwinian theory of descent, which he specifically attacked in Wahrheit und Flachheit des Darwinismus (Nördlingen, 1872). The natural consequence of this individuality of opinion was that his books were practically disregarded, and Planck was deeply incensed. The ill success of Die Weltalter nerved him to new efforts, and he repeated his views in Katechismus des Rechts (1852), Grundlinen einer Wissenschaft der Natur (1864), Seele und Geist (1871), and numerous other books, which, however, met with no better fate. In the meantime he left Tubingen for Ulm, whence he came finally to the seminary of Maulbronn. He died on the 7th of June 1880 in an asylum after a short period of nervous prostration. After his death a summary of his work came into the hands of K. Köstlin (author of Aesthetics, 1869), who published it in 1881 under the title Testament eines Deutschen, Philosophie der Natur und der Menschheit. Planck’s views were elaborately developed, but his method of exposition told heavily against their acceptance. He regarded himself as the Messiah of the German people.

Beside the works above quoted, he wrote System des reinen Idealismus (1851); Anthropologie und Psychologie auf naturwissenschaftlicher Grundlage (1874); a political treatise, Bismarck: Süddeutschland und der deutsche Nationalstaat (1872); and Logisches Causalgesetz und natürliche Zweckmässigkeit (1874).

See Umfrid, Karl Planck, dessert Werke und Wirken (Tübingen, 1881); and Schmidt, “Das Lebensideal Karl Christian Plancks,” in the Vorträge der philosophischen Gesellschaft (Berlin, 1896).

PLANE. 1. In botany, the common name of a handsome tree known botanically as Platanus orientalis, a native of Greece and western Asia, a favourite shade-tree of the ancient Greeks and Romans, and introduced by the latter to south-west Europe. Plane (Platanus orientalis).

1, Leaf, nat size.

2 and 3, Base of leaf-stalk showing bud-protecting cap, about nat. size.

4, Male, 5, Female inflorescence.

6, Head of fruits, about nat. size.

7, A fruit with enclosed seed, cut lengthwise.

It is one of the most successful trees in London and other large towns; the smooth face of the leaf is easily washed by rain; and the periodical peeling of the bark also serves to get rid of impurities. It is a large tree with widely spreading branches and alternate, palmately five-lobed leaves, resembling those of the sycamore in shape, but quite hairless and of a brighter green. The bud in the leaf axil is protected during its development by the hollow base of the leaf-stalk, which lifts off like an extinguisher when the leaf falls in autumn. The minute, unisexual flowers are borne in dense pendulous heads, which contain either male or female flowers; the small one-seeded fruits are densely crowded in a ball, from which they gradually separate in drying, and are readily carried by the wind. The wood, which is hard and heavy, though not strong, is used in Persia and other countries of western Asia for house construction and furniture. A variety of forms are known in cultivation, the commonest being the maple-leaved (acerifolia), the London plane, which has usually three-lobed leaves; var. laciniata has very deeply much divided leaves, and var. variegata, variegated foliage. Platanus occidentalis, an allied species, is a native of the United States, being most abundant and growing to its largest size in the bottom lands of the basins of the lower Ohio and the Mississippi rivers. It was introduced into England early in the 17th century, and is occasionally met with in western and central Europe. Professor C. S. Sargent (Silva of North America) refers to it as the most massive if not the tallest, deciduous-leaved tree of the North American forest; it is known in America as sycamore and buttonwood. It differs from P. orientates in its less deeply lobed, more leathery pubescent leaves and in the usually solitary balls of fruit.

2. The name of a carpenter’s hand-tool, used for levelling and smoothing (Lat. planus, level) the surface of wood. The machine tool used for a similar purpose for metals is generally known as a planing-machine or planer.

PLANET (Gr. , a wanderer), in the ancient astronomy, one of seven heavenly bodies characterized by being in motion relative to the fixed stars, which last appeared immovable upon the celestial sphere. As thus defined the planets were the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn. In modern astronomy since Copernicus, the term is applied to any opaque body moving around the sun. Taken in its widest sense it applies to the satellites which are sometimes termed secondary planets. Each of these moves around a planet larger than itself, which it accompanies in its revolution round the sun. A planet not revolving round another is termed a primary planet.

The primary planets are classified as major and minor. The former are eight in number and, with the sun, form the principal members of the solar system, under which head their arrangement is described. The earth on which we live is the third in the order of the major planets from the sun. With respect to the positions of their orbits relative to the earth, the other planets are distinguished as inferior and superior. The former, only two in number, comprise Mercury and Venus, which revolve between the earth and the sun. The superior planets are those whose orbits are outside that of the earth. The synodic revolution of an inferior planet is the time in which it performs a revolution relative to the line joining the earth and the sun. This is greater than its actual time of revolution. The phases or appearances presented by such a planet depend upon its configuration with respect to the earth and sun, and therefore go through their complete periods in a synodic revolution. At superior conjunction the illuminated hemisphere of the planet is presented to the earth so that it presents the form of a full moon. As it moves towards inferior conjunction, the lines from the planet to the sun and to the earth, or the angle sun-earth as seen from the planet, on which the phase depends, continually make a greater angle. At the time of greatest elongation this angle is 90°, and the planet appears one half illuminated, like the moon at first or last quarter. Then, as it approaches inferior conjunction, the visible portion of the disk assumes the crescent form, and while the circle bounding the disk continually increases owing to the approach of the planet to the earth, the crescent becomes thinner and thinner until, near inferior conjunction, the planet is no longer visible. After conjunction the phases occur in the reverse order. The brilliancy of the planet, as measured by the total amount of light we receive from it, goes through a similar cycle of change. The point of greatest brilliancy is between inferior conjunction and greatest elongation. In the case of Venus this phase occurs about three or four weeks before and after inferior conjunction.