INCLINATION OF THE EARTH'S AXIS. 105 



CHAPTER IX. 



The Seasons. 



"These, as they change, Almighty Father, these 

 Are but the varied God. The rolling year ' 

 Is full of thee. " Thompson. 



THROUGHOUT the preceding chapter, we have spoken of the 

 plane of the orbit of the earth as inclined to the plane of the equa- 

 tor. As a necessary result of this, the axis of the earth points, at 

 all times, towards the same point of the heavens, with the ex- 

 ception of the slight motion caused by the precession of the 

 equinoxes. This is a fact, with which we are all familiar, for we 

 know the pole star is the star towards which the axis of the earth 

 points throughout the year. Thus, in the following diagram, let 



A B C D, represent the earth in four different positions in its 

 orbit. Now, if the axis of the earth was perpendicular to the plane 

 of the orbit, as shown in the diagram, then the plane of the equa- 

 tor, a, I, would correspond with the plane of the orbit, but, as the 

 plane of the equator manifestly does not correspond with the plane 

 of the ecliptic, the axis of the earth must be inclined to the plane 

 'of its orbit, as in the next diagram, and this inclination it main- 

 tains throughout its entire revolution around the sun, its axis 

 always pointing towards the polar star. Of course, in our diagram, 

 this does not appear to be strictly the case, as we cannot repre- 

 sent the star removed to a sufficient distance. The inclination of 

 the axis of the earth to the plane of the sun's apparent path, is the 

 cause of all the variety of the seasons ; of the differing lengths 

 of the nights and days ; and the daily changes of the sun's decli- 

 nation. If the earth's axis had been placed perpendicular to the 



