204 THE CHANGING SEASONS. 



corresponding portion of the darkened hemisphere, which 

 advances beyond the South Pole to invade the illuminated, 

 I have but to occupy at noon, on the 2ist of June, a point of 

 the same equatorial prolongation. Six months later, the same 

 spectacle will be presented, inversely, on the 2ist of December, 

 in the southern hemisphere. See Fig. 43 #, where the pole N 

 indicates the six months' day of the northern hemisphere (from 



the spring to the autumn 

 equinox) ; while in Fig. 43 

 b, the pole S indicates the 

 six months' night of the 

 ~ northern hemisphere (dur- 



FIG. 43. The Six Months' Day and Night. 



ing the same period). 



Now, no effort of the imagination is required to understand 

 why the inhabitants of the northern hemisphere enjoy summer 

 while those of the southern are enduring winter ; why it is 

 "blossoming spring" to the former when it is " purple 

 autumn" to the latter, and vice versa. Equally easy is it 

 to comprehend why, after the equinox, day, or the duration 

 of the sun above the horizon, gradually diminishes in one 

 hemisphere and increases in the other; why, in summer, 

 and in both hemispheres, the longest days alternate with 

 the shortest nights, and in winter, the longest nights with 

 the shortest days. It will not be more difficult to explain 

 the cause of the prevailing cold in the polar zones, despite 

 the prolonged sojourn of the sun above the horizon for a 

 great part of the year. Observe how obliquely the solar 

 rays are directed towards yonder shrouds of ice and snow : 



