340 PHYSIOGRAPHY. [chap. 



The poles would be the coldest parts ; and all points of the 

 surface, at equal distances from the poles, would be equally- 

 warmed and equally illuminated ; while the winds, arising 

 from the lower currents, would be directed obliquely, from 

 the poles towards the equator, and those formed by the 

 upper currents would blow in the contrary direction. 



Suppose, once more, that the axis were neither in the 

 position indicated in the first, nor in that shown in the 

 second diagram, but that it occupied some intermediate 

 position, such as is represented in the third figure. Here 

 it is plain, that the one pole, which is turned towards the 

 sun, would always be enjoying a good supply of light and 

 heat, while the opposite pole, which is turned away from 

 the sun, would be in everlasting darkness and cold. 



As a matter of fact, the axis of our earth is in the position 

 represented in the last case ; but in consequence of other 

 movements, which will be duly explained, no part of the 

 surface is permanently dark and cold. 



If the stars be watched on a cle?r night, for a short time, 

 it will be observed that they appear to move across the 

 heavens, from the east to the west, in the same way as the 

 sun does during the day ; and, if any one of these stars were 

 bright enough to cast a shadow, we might make a star-dial 

 for the night, just as sun-dials are made for the day. If the 

 star were one of those which never set in England, such, for 

 example, as the star in the end of the tail of the Great Bear 

 (Fig. i), its shadow would, in the course of the night, sweep 

 over a segment of a circle, just as the shadow cast by 

 the sun sweeps over a segment of a circle during the day. 

 Suppose the circle to be completed, and to be divided 

 into 86,164 equal parts; then, observation would show that 

 the shadow thrown by the star travels over these equal 

 parts in equal periods of time, and each such period is 



I 



