5 6 The Realm of Nature CHAP. 



the Equator, and it is the only great circle the plane of 

 which cuts the axis at right angles. The half of the globe 

 in which the north pole is situated is termed the northern 

 hemisphere ; the half whose centre is the south pole is the 

 southern hemisphere. Great circles running through the 

 poles, and therefore having a north and south direction, 

 are called meridians. The direction toward which the Earth 

 turns is called the east, that from which it turns the west. 

 East and west thus indicate merely a direction of turning, 

 and do not refer to fixed points. Small circles traced round 

 the Earth, their planes cutting the axis at right angles, 

 have thus an east and west direction and are called parallels. 

 They are, of course, smaller and smaller as the poles are 

 approached. The equator, meridians, and parallels are 

 well shown on the map of the world in hemispheres (Plate 

 XIV). 



92. Latitude is the name given to the angular distance 

 at the centre of any point on the Earth's surface from 

 the equator measured toward the poles. The equator is 

 chosen as o of latitude, and as the distance of the poles 

 is a quarter turn or right angle ( 31) the north pole 

 has latitude 90 N., the south pole latitude 90 S. The 

 latitude of any place, except the poles, merely refers to the 

 distance from the equator of a small circle, or parallel of 

 latitude, passing through the place in question. Latitude 

 is always measured astronomically by observing the altitude 

 of the pole of the heavens, directly or indirectly. The 

 altitude of the pole, or its angular distance above the 

 horizon of an observer, is equal to the angular distance of 

 the observer from the Earth's equator. Standing on the 

 equator an observer (if the effects of refraction are not 

 considered) would see the north pole of the heavens close 

 to the pole star on the northern horizon, and the south pole 

 of the heavens on the southern horizon, while all the stars 

 would appear to rise in the eastern half of the sky, to 

 describe vertical semicircles, and sink on the western side. 

 If the observer were to journey farther north he would lose 

 sight of the south pole of the heavens, while the north pole 

 would rise higher and higher above the horizon. By the 



