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Rh the sphere of projection. The term is also applied to a point from which lines radiate, as, for instance, the origin in a system of polar co-ordinates, or the common point of a pencil of rays. In the geometry of conic sections the “pole” of a line, termed the “polar” of the point, is the intersection of the tangents (either real or imaginary) at the points where the line meets the conic (see : § Projective). The “magnetic poles” of the earth are the points on the earth’s surface where the dipping needle is vertical (see ), and the “poles” of a magnet are the points of the magnet where the magnetic intensity is greatest. In electricity, the term is applied to the elements of a galvanic (q.v.), or to the terminals of a frictional electrical machine.  POLECAT, the common name given to any member of the Musteline genus Putorius (see ). The polecats form a small group confined to the northern hemisphere, of which the best known and most widely distributed is the common polecat of Europe (P. foetidus or P. putorius). This animal, at least so far as its disposition, size and proportions are concerned, is well known in its domesticated condition as the ferret, which is but a tamed albino variety of the true polecat. The colour of the latter, however, instead of the familiar yellowish-white of the ferret, is of a dark brown tint above and black below, the face being variegated with dark brown and white markings. Its skull is rough, strongly ridged, and altogether of a far more powerful type than those of the stoats, weasels or martens, the skull of the female is very much smaller and lighter than that of the male. The fur is long, coarse, and of comparatively small value, and changes its colour very little, if at all, at the different seasons of the year.



The polecat ranges over the greater part of Europe, reaching northwards into southern Sweden and in Russia to the region of the White Sea. It does not occur in the extreme south, but is common everywhere throughout central Europe. In the Alps 1t ranges far above the tree-line during the summer, but retreats in winter to lower ground. It is confined to the northern counties of England and Scotland, where it is becoming very rare, owing to persecutions from game-keepers, and in Ireland it appeals to be extinct. In fine weather it lives either in the open air, in holes, fox-earths, rabbit-warrens, under rocks or in wood-stacks, while in winter it seeks the protection of deserted buildings, barns or stables. During the day it sleeps in its hiding place, sallying forth at night to plunder dovecots and hen-houses. It climbs but little, and shows far less activity than the marten. It feeds ordinarily on small mammals, such as rabbits, hamsters, rats and mice, on such birds as it can catch, especially poultry and pigeons, and also on snakes, lizards, frogs, fish and eggs. Its prey is devoured only in its lair, but, even though it can carry away but a single victim, it commonly kills everything that comes in its way, often destroying all the inhabitants of a hen-house in order to gratify its passion for slaughter. The pairing time is towards the end of the winter, and the young, from three to eight in number, are born in April or May, after a period of gestation of about two months. The young, if taken early, may be easily

trained, like ferrets, for rabbit-catching. The polecat is very tenacious of life and will bear many severe wounds before succumbing; it is also said to receive with impunity the bite of the adder. Its fetid smell has become proverbial. To this it is indebted for its generic name Putorius (derived, as are also the low Lat. putacius, Fr. putois, and Ital. puzzola, from puteo), as well as the designation foumart (i.e. foul marten) and its other English names, fitchet, fitchew. Attempts to account for the first syllable of the word polecat rest entirely on conjecture.

The Siberian polecat (Putorius eversmanni) is very like the European in size, colour and proportions, but with head and back both nearly or quite white, and skull more heavily built and sharply constricted behind the orbits, at least in fully adult individuals. It inhabits the greater part of south-western Siberia, extending from Tibet into the steppes of south-eastern European Russia.

The black-footed or American polecat (Putorius nigripes) is a native of the central plateau of the United States, and extends southwards into Texas. It is often called the prairie-dog hunter, as it is nearly always found in the warrens of that animal. The fur is cream-yellow, the legs are brown, and the feet and tail-tip black.

The mottled polecat (Putorius sarmaticus), a species occurring in southern Russia and south-western Asia, and extending from eastern Poland to Afghanistan, differs from other polecats both by its smaller size and its remarkable coloration, the whole of the upper-parts being marbled with large irregular reddish spots on a white ground, while the under-side, limbs and tail are deep shining black. Its habits appear to be much like those of the common polecat.

 POLENTA, DA, the name of a castle in Romagna, from which came the noble and ancient Italian family of Da Polenta. The founder of the house is said to have been Guido, surnamed l'Antico or the Elder, who wielded great authority in Ravenna in the 13th century. His grandson Guido Novello upheld the power of the house and was also capitano del popolo at Bologna; he was overthrown in 1322 and died the following year. His chief claim to renown lies in the fact that in 1321 he gave hospitality to the poet Dante, who immortalized the tragic history of Guido’s daughter Francesca, unhappily married to Malatesta, lord of Rimini, in an episode of the Inferno. Guido’s kinsman Ostasio I. was lord of Cervia and Ravenna from 1322 to 1329, and, after being recognized as a vassal of the Holy See, again became independent and went over to the house of Este, whom he served faithfully in their struggles with the Church until his death in 1346. His son Bernardino, who succeeded him as lord of Ravenna in 1346, was deposed in 1347 by his brothers, Pandolfo and Lamberto II., but was reinstated a few months later and ruled until his death in 1359; he was famous for his profligacy and cruelty. His son Guido III. ruled more mildly and died in 1390 Then followed Ostasio II. (d. 1396), Obizzo (d. 1431), Pietro (d. 1404), Aldobrandino (d. 1406), all sons of Guido III. Ostasio III. (or V.), son of Obizzo, was at first allied with the Venetians; later he went over to the Milanese, and, although he again joined the Venetians, the latter never forgave his intrigue with their enemies, and in 1441 they deprived him of his dominions. He died in a monastery in 1447.  POLE-VAULTING, the art of springing over an obstacle with the aid of a pole or staff. It is probable that an exercise of the kind was a feature of Greek gymnastics, but with this exception there is no record of its ancient practice as a sport. As a practical means of passing over such natural obstacles as canals and brooks it has been made use of in many parts of the world, for instance in the marshy provinces along the North Sea and the great level of the fens of Cambridgeshire, Huntingdonshire, Lincolnshire and Norfolk. The artificial draining of these marshes brought into existence a network of open drains or canals intersecting each other at right angles. In order to cross these dryshod, and at the same time avoid tedious roundabout journeys over the bridges, a stack of jumping poles was