POL 



POL 



1. The first sixteen of these interme- 

 diate points are named as follows : — 

 Half-way between north and east, is 

 North-East (n.e.) ; and similarly are 

 explained South-east. South-west, and 

 North-West (s.e., s.w., n.w.)- Again, 

 half-way between North and North-East 

 is North-North-East (n.n.e.); and thus 

 are explained East- North-East, East- 

 South- East, South-South-East, South- 

 South-West, West-South-West, West- 

 North-West, North-North-West (e.n.e., 



E.S.E., S.S.E., S.S.W., W.S.W., W.N.W., 



N.N.W.). 



2. These sixteen are subdivided, the 

 new and final subdivisions being de- 

 scribed each by the simplest of the two 

 adjacent directions, and the cardinal 

 direction in which that last direction Is 

 left. Thus, North-East by North means 

 the direction next to North-East in going 

 towards the north, and comes between 

 N.E. and N.N.E. By the same rule. 

 North-east by North might be called 

 North-North-East by East, but the former 

 is the more simple. 



3. The angle of revolution from one 

 point to the next is, of course, the 32nd 

 part of 360°, or 11 J°, and it is sometimes 

 customary to insert fractions of a point ; 

 thus n.n.eJe., means a quarter of a 

 point eastward from n.n.e. 



POLAR CIRCLES. Two circles. 

 North and South, Arctic and Antarctic, 

 described by the earth in its diurnal 

 rotation, and so named from their proxi- 

 mity to the two poles, from which they 

 are at the same distance as the tropics 

 are from the equator, viz. 23^ degrees. 

 These polar circles bound those portions 

 of the earth where it is continuous day 

 and night during several diurnal revolu- 

 tions of our planet. On the terrestrial 

 globe these circles surround the frozen 

 zones. 



PO'LARISCOPE. An instrument con- 

 trived for the exact and convenient ob- 

 servation of the phenomena of polarized 

 light, and also for the measurement of 

 the angle of polarization. 



POLA'RITY. A term applied, in its 

 most comprehensive sense, to a body 

 possessing certain powers which are not 

 general, but local, and not the same, but 

 opposite. It is more particularly applied 

 to the magnet, the attractive power of 

 •which is not possessed in an equal de- 

 gree by every particle composing the 

 magnet, but is chiefly localized in two 

 points at or near its extremities ; fur- 

 ther, the powers residing in these points 

 205 



are not one and the same, but different 

 —indeed contrary in their nature, and 

 are distinguished by the different names 

 of Boreal magnetism and Austral mag- 

 netism. These two points are called the 

 poles of the magnet, and the right line 

 joining them is the axis. 



1. Polarity, Chemical. The principle 

 just stated has been applied to the che- 

 mical phenomena of the voltaic circle. 

 The zinc and hydrochloric acid are 

 equally supposed to have a polarizable 

 molecule: one pole of each molecule has 

 the attraction, or affinity, which is cha- 

 racteristic of zinc, or zincous attraction, 

 and is called the zincous pole ; while the 

 other has the attraction, or affinity, which 

 is characteristic of chlorine, or chlorous 

 attraction, and is called the chlorous 

 pole. Polarity is not an ordinary condi- 

 tion of the particles of either the zinc or 

 the acid ; but is developed in both when 

 brought into contact with each other. 



2. Two Polarities. A term expressive 

 of two antagonist energies, each of which 

 repels that which is similar, and attracts 

 that which is opposite, to itself. Thus, the 

 two north or two south poles of two mag- 

 netic needles mutually repel each other; 

 but the north pole of one needle, and the 

 south pole of another, mutually attract 

 each other. 



3. Reversion of Terms. The earth it- 

 self being considered as a magnet, or as 

 containing within itself a powerful mag- 

 net, lying in a position nearly coinciding 

 with its axis of rotation, the south pole of 

 a magnetic needle would point towards 

 the north pole of the earth ; so that the 

 north end is the south pole, and the south 

 end the north pole of a magnetic needle. 



4. Boreal and Austral Polarities. To 

 avoid the above confusion of terms, the 

 words Boreal and Austral have been 

 applied to the magnetism of the earth, 

 while the terms North and South have 

 been restricted to that of the needle ; 

 what had been called northern polarity 

 being now Austral polarity ; what had 

 been called southern, being Boreal po- 

 larity. 



5. Chemical and Cohesive Polarities. 

 Two hypothetical forces, supposed by 

 Dr. Prout to reside in the ultimate mole- 

 cules of matter ; the chemical being of a 

 binary character, existing between mole- 

 cule and molecule, and chiefly between 

 molecules of different matter ; the cohe- 

 sive determining, under certain circum- 

 stances, the cohesion of the molecules 

 of the same matter. 



N 



