POL 



POL 



POLARIZED LIGHT. A ray of light 

 is said to be polarized, when, after its 

 emergence from the substance, or reflec- 

 tion from the surface, of a body, it ac- 

 quires poles or sides with different pro- 

 perties in relation to the plane of its 

 incidence. Polarized light is procured — 

 L by reflection from the surfaces of 

 transparent and of opaque bodies ; 2. by 

 transmission through several plates of 

 uncrystallized bodies ; and, 3. by trans- 

 mission through bodies regularly crystal- 

 lized, and possessing the property of 

 double refraction, as Iceland spar. 



POLE (TToXew, to turn). The extre- 

 mity of the axis of a circle. The extre- 

 mities of the axis of the earth are termed 

 the poles, and are, respectively, the 

 north and south— the Arctic and Ant- 

 arctic— i)o\es of our globe. The earth's 

 axis, being extended each way, becomes 

 an axis to the spherical concavity of the 

 sky, and its extremities are the north 

 and south poles of the heavens. See 

 Axis. 



Pole of revolution. When a globe re- 

 volves about one of its diameters, each 

 extremity of that diameter is called a 

 pole of revolution. Every point of the 

 sphere describes either the great circle 

 which has the poles of revolution for its 

 poles, or one of the parallels of that 

 great circle. 



POLE-STAR, or POLAR STAR. A 

 bright star of the second magnitude, in 

 the tip of the tail of the northern con- 

 stellation Ursa Minor, or the Little Bear ; 

 it is named from its proximity to the 

 north pole of the heavens, the only one 

 visible in our latitude. 



PO'LEMOSCOPE (TToXejiiop, war, o-ko- 

 Treo), to view). An instrument, invented 

 by Hevelius, for viewing objects which 

 cannot be seen by direct vision. It con- 

 sists of a perspective glass, having a 

 reflector placed at an angle of 45° to its 

 axis, so that any object falling on the 

 reflector is conveyed to the eye. The 

 name suggests that a person might, by 

 means of such an instrument, observe, 

 from a place of concealment, what is 

 going on in an enemy's camp. 



POLITICAL ECONOMY. That branch 

 of political science which relates to the 

 production and accumulation of wealth, 

 its distribution and consumption. It is, 

 in short, to the state what private eco- 

 nomy is to the sinjfle family. 



POLLEN. The organic matter by 

 which impregnation is effected in the 

 vegetable kingdom. It consists of fine 

 266 



powder, or grains, enclosed within the 

 anther. Each grain, when mature, and 

 brought into contact with the stigmatic 

 tissue, emits a tube, containing a fluid 

 termed fovilla, which is charged with 

 molecular matter. The pollen-masses of 

 Orchidaceous and Asclepiadaceous plants 

 consist of pollen-grains cohering into 

 solid waxy masses. 



POLLUX. A star of the second mag- 

 nitude, in the zodiacal constellation Ge- 

 mini. The same name is also given to 

 the hindermost twin, or posterior part, 

 of the same constellation. 



POLY-, POL- (7ro\u9, many). A 

 Greek prefix, denoting many or much. 



1. Polakenium. A term applied by 

 Richard to a fruit consisting of several 

 akenia (see AchcBnium). When there are 

 two cells, the fruit is a di-akenium ; when 

 three, a tri-ahenium ; and so on. 



2. Poly-adelphia (ade\06?, a brother). 

 The eighteenth class of plants in the 

 Linnaean system, in which the stamens 

 are associated in several parcels, or 

 brotherhoods, as in Hypericum. 



3. Poly-andria (ui/Jjp, a man). The 

 thirteenth class in the Linnaean system 

 of plants, comprising those which have 

 more than twenty stamens inserted be- 

 neath the ovarium. 



4. Poly-basite. A double sulphuret of 

 silver and other metals, in which the 

 sulphuret of silver and the subsulphuret 

 of copper, being isomorphous, replace 

 each other in indeterminate proportions. 



5. Poly-carpous {Kapno^, fruit). A term 

 applied to a plant which has the power of 

 bearing fruit many times without perish- 

 ing. Poly-carpous plants are distinguished 

 into the caulocarpous, or those whose 

 stem endures many years, constantly 

 bearing flowers and fruits, as trees and 

 shrubs; and the rhizocarpous, or those 

 whose root endures many years, but 

 whose stems perish annually, as herba- 

 ceous plants. 



6. Poly-chorion (xoptov, any skin). A 

 term applied by Mirbel to the fruit of 

 the ranunculus, &c., more commonly 

 known by the term etcerio. 



7. Polychroite {xpo°^i colour). The 

 extractive matter of saffron, the watery 

 infusion of which assumes diflTerent co- 

 lours when treated with different agents. 



8. Poly-clinum {KKivr\, a bed). A gene- 

 ral term applied by Cuvier to all those 

 forms of aggregated tunicated mollusca, 

 which agree more or less closely, in inter- 

 nal structure, with the salpae and as- 

 cidians. 



