f>18 



POLYHALITE POLYPI. 



were several pictures. His works were probably 

 mi wood. Polygnotus is represented as being the 

 first who made painting independent of sculpture, 

 and gave life, motion, character and expression 

 (whence his surname nfe<y?etf<>() to the countenance, 

 skilful disposition to (he drapery, and proportion to 

 the figures, and he is said to have been the first 

 who painted tetrac/iromes (pictures with four 

 colours). With him begun the grand and lofty 

 style in Greek painting. 



POLYHALITE ; the name of a mineral species, 

 bestowed in allusion to the many salts which it con- 

 tains. It occurs in coarsely fibrous masses of a 

 reddish white colour, and a pearly lustre ; specific 

 gravity 2.77 ; hardness not much above that of 

 gypsum. Its constituents are as follows : 



Hydrous sulphate of lime, . 

 Anhydrous do. . . . . 



Anhydrous sulphate of magnesia. 

 Sulphate of putasli, .... 



Muriate of soda, 

 Ked uxide of irou, 



2825 



22.42 



20.03 



27.07 



.1!) 



.34 



It occurs iu the salt mines of Ischel, in Upper 

 Austria. 



POLYHEDRON, OR POLYEDRON; a body or 

 solid contained by many rectilinear planes or sides. 

 When the sides of the polyhedron are regular poly- 

 gons, all similar and equal, -then the polyhedron 

 becomes a regular body, and may be inscribed in a 

 sphere; that is, a sphere may be described about it. 

 so that its surface shall touch all the angles or cor- 

 ners of the solid. There are but five of these regu- 

 lar bodies, viz. the tetrahedron, the hexahedron or 

 cube, the octahedron, the dodecahedron, and the 

 icosahedron. 



TOLYHISTOR (from <rx w , much, and 'itr^, 

 knowing) ; a scholar who is acquainted with all the 

 chief branches of science. Formerly it was possible 

 to be well versed, at the same time, in law, theology, 

 tuediciiie, &c. (as in the case of Leibnitz, and seve- 

 ral scholars of eminence before him.) In the pre- 

 sent advanced state of science, it is impossible to be 

 a polyhistor without the sacrifice of thoroughness. 

 Polyhistor is also used for a scholar, who, besides 

 his peculiar branch, has a general knowledge of 

 most others. See Morhof. 



POLYHYMNIA, OR POLYMNIA ; according 

 to the later poets, the muse of lyric song or of music, 

 to whom is attributed the invention of mimes and 

 pantomimes. The Grecian artists represented her 

 covered with a veil, and in a meditating posture. 

 Her attributes are the lyre and the plectrum. She 

 places the forefinger of her right hand on her mouth, 

 or holds a scroll. 



POLYMIGNITE; the name of a mineral recently 

 found in Norway. It is black, brilliant, and crys- 

 tallized in small prisms, long, thin, with rectangular 

 bases, the edges of which are commonly replaced by 

 one or several planes. Specific gravity, 4.806. It 

 scratches glass. Fracture conchoidal, without indi- 

 cations of cleavage; lustre semi-metallic. Alone, 

 before the blow-pipe, it undergoes no change, but 

 melts easily with borax. Its composition is as 

 follows: 



Titanic acid, 



Zirconia, 



Oxide of iron. 



Lime, 



Oxide of manganese, 



Oxide of cerium, 



Yttria, 



48.3 

 14.4 



12.2 

 4.2 



2.7 



5. 



11.5 



Traces of magnesia, potash, silex and oxide of tin, 96.3 



It is found in the zircon sienite at Fredericksvoern. 

 POLYNESIA (from rXuf, many, and vyn>s, 

 island) ; the name given by geographers to the 

 great body of islands scattered over the Pacific 

 ocean, between Australasia and the Philippines, 



and the American continent. It extends from lat. 

 ^5 N. to 50 S.; and from Ion. 170 to 230 E., 

 an extent of 5000 miles from north to south, and ot 

 3600 from west to east. If. includes, therefore, the 

 Sandwich islands, the Marquesas, Navigator'?, So- 

 ciety, Mulgrave, Friendly, Ladrone, and Pelewisles> 

 the Carolines, Pitcairn's island, &c. See these arti- 

 cles, and also, Australia, Oceanica, and Pacific 

 Ocean. 



PO L YN I C ES. See Eteodes, and Thebes. 



POLYPHEMUS, son of Neptune, the most 

 famous of the Sicilian Cyclops, is described by 

 Ulysses (Odyssey ix.), as a giant, living by himself 

 in a cave, and feeding his flocks. Ulysses (q. v.) 

 and his companions, having unwarily taken refuge 

 in his cave, were found there by Polyphemus, when 

 he returned home at night, and shut up the mouth 

 of the cavern with a large stone. Having seized 

 two of the strangers, he ate them for supper, and 

 the next morning made a breakfast of two more of 

 tiiem, after which he drove out his flocks to pasture, 

 and shut up the unhappy captives by closing the 

 entrance of his cave. Ulysses then contrived a plan 

 for their escape. Having sharpened the club of the 

 Cyclops, he intoxicated the monster with wine, and, 

 as soon as he fell asleep, bored out his eye. He 

 then tied himself and his companions under the 

 bellies of the sheep, in which manner they passed 

 safely out in the morning. Polyphemus was the 

 lover of the nymph Galatea, but the nymph despised 

 his offers, and preferred Acis, who was killed by 

 his jealous rival. See Galatea. 



POLYPI, in natural history; this forms the 

 thirteenth class of the invertebrate animals, and is 

 one of the largest and most remarkable of the animal 

 kingdom. The animals which it comprehends are 

 gelatinous, with elongated contractile bodies, and 

 an alimentary sac with but one opening ; a distinct 

 and terminal mouth, surrounded with tentacula, 

 or radiated lobes ; the greater part of which are 

 adhering together, and forming compound animals. 

 These animals are of the simplest kind, possessing 

 an organization so low in the scale of being that 

 they appear almost incapable of reproducing their 

 kind. They are destitute of a head and eyes, and 

 are provided with no organs fitted for circulation, 

 respiration, or locomotion. The bodies of these 

 animals appear only a homogeneous mass, consti- 

 tuted of a gelatinous and irritable cellular tissue, in 

 which the vital fluids move in a slow and protracted 

 course. The whole animals of this extensive class 

 are provided with an internal cavity or stomach, 

 and some, of them with indistinct traces of hollow 

 canals and ovaries. The body is usually of a cylin- 

 drical or conical form, of a gelatinous or transparent 

 texture; the mouth is the only opening, and is sur- 

 rounded by tentacula, varying in form and number. 

 So universally diffused is the principle of life through 

 the simple structure of the polypi, that portions of 

 them may be severed, and these portions, if allowed 

 to remain in their proper element, will soon become 

 perfect animals, with all the functions fully deve- 

 loped, as in the individual from which they were 

 cut off. The hydra will sometimes of its own ac- 

 cord split into two ; each division becoming inde- 

 pendent of the other, and growing to the same size 

 as the original hydra. Trembley found that diffe- 

 rent portions of one polypus might be ingrafted on 

 another, by cutting their surfaces and pressing them 

 together; for by this means they quickly unite, and 

 become a compound animal. When the body of 

 one hydra is introduced into the mouth of another, 

 so that their heads are kept in contact for a suffi- 

 cient length of time, they unite and form but one 

 individual. A number of heads and bodies may 



