XX.] 



THE MOVEMENTS OF THE EARTH. 



339 



first diagram in Fig. in, where the axis is represented by a 

 thick line, and the sun, which must be supposed to be at a 

 very great distance, is represented by a small circle. Then, 

 it is clear, that the same half of the earth would always be 

 turned towards the sun ; and the only effect of the twirling 

 round would be to modify the direction of the winds, in a 

 manner which will be explained presently. But now suppose 



Fig. III. — Diagram to illustrate effect of changing the position of the eartli's a.\is 

 in relation to the sun. 



that the axis were perpejidicularX.o a prolonged radius of the 

 sun, as represented in the second diagram : then the rotation 

 of the earth would bring different parts of the surface, in 

 succession, towards the sun, and they would thus become, in 

 turn, illuminated and warmed. In fact, the rotation would 

 produce the alternation of day and night; and the days and 

 nights would be equal all over the world, and at all times. 



Z 2 



