84 OUTLINES OF NATURAL PHILOSOPHY. 



b. As the sun passes to the north, the circle of illu- 

 mination inclines also to the north ; the sun ap- 

 proaches nearer to the zeniths of all the places in 

 the northern hemisphere, and retires by the same 

 quantity from the zeniths of all the places in the 

 southern. The days lengthen in the former hemi- 

 sphere, and shorten in the latter. 



c. In the Northern Frigid Zone, over a space equal 

 to the sun's declination, the sun does not set ; and 

 over an equal space in the Southern, he does not 

 rise. 



d. When the sun arrives at the Northern Tropic, he 

 has approached as near as he can to the zenith of 

 every place between the Northern Tropic and the 

 Pole, and has receded the farthest from the zenith 

 of every place in the southern hemisphere. The 

 days are the longest in all the former of these ; the 

 shortest in the latter. Within the whole of the 

 arctic circle, the sun does not set on the solstitial 

 day ; and within the whole of the antarctic, he does 

 not rise. It is the Summer Solstice in the one he- 

 misphere j the Winter Solstice in the other. 



e. The same vicissitudes take place in a contrary di- 

 rection, as the sun passes to the Southern Tropic. 



f. The four points, the two Equinoxes and the two 

 Solstices, divide the year into the four Seasons. 

 The positions of the circle of illumination at these 

 four times are represented^ figs. 9, 10, J 1. 



g.The 



