222 SEASONS. [Lessen xxxw. 



darkened hemisphere, and the southern one in 

 the enlightened part; our day is at the shortest, 

 while in the southern hemisphere the clay is lon- 

 gest; our Winter commences and their Summer; 



. being about the 21st of December. As the mo- 

 tion of the globe is continued, our days lengthen ;. 

 and when it has again arrived at the intersection 

 of the hoops, we have Spring, and the inhabitants 

 of the southern hemisphere have Autumn. In 

 the course of this experiment it will be found, that 

 ach of thepoles continues enlightened half through 

 the annual revolution, and darkened through the 

 other half: consequently, at the poles of the 

 earth, there is but one day and one night through 

 the year. 



At the equator the sun's rays fall perpendicu- 

 larly on the earth, and therefore act more 

 powerfully; whence arises the great heat* of the 

 torrid zone. On advancing towards both poles,, 

 the rays fall more and more obliquely, and 

 therefore act with less force and less; whence 

 this -space is occupied, first by the temperate 



.zones extending on each side the tropics, and then 

 by the frigid zones extending from these to the 

 poles. So weak is the sun's power in these last 

 owing to the great obliq-uity with which its rays 

 strike the earth, that they are buried in almost 

 perpetual snow and ice. But these are merely 

 the differences of climate: the differences of 

 Season depend not upon these causes merely, 

 but also upon the length of time that any por- 

 iion of the earth is exposed to the solar rays. 



During 



