THE EARTH'S ROTATION 25 



(B) Now make the axis on which the globe rotates parallel to the 

 line joining the centers of the globe and light. (Figure 5, B.) 

 Rotate the globe. How much of the globe is illuminated by the 

 light? Is the same part illuminated all the time? Does any 

 place receive light for a longer time during a rotation than any 

 other place on the globe ? Remove the globe to the opposite side 

 of the light without changing the direction of its axis. When 

 the globe is rotated, is there any 



change in its illumination? If 

 so, what ? 



(C) Place the globe so that 

 its axis is inclined about 25 

 degrees from the perpendicular 

 to the line joining the centers 

 of the globe and light. (Figure 

 5, C.) Rotate the globe. How 

 much of it is illuminated? Is 

 the same part illuminated all 

 the time? Do any places in 

 the illuminated part receive 

 light for a longer time during 



a rotation than other places ? FlGURE 5.- RELATIVE POSITIONS OP 



Remove the globe to the op- GLOBE AND LIGHT 



posite Side of the light with- Corresponding to A, B, and C of 



out changing the direction of Experiment 4. 



its axis. When the globe is 



rotated, is there any change in the length of time of illumination 



of the places before noted? If so, what? 



As was seen in the previous experiment, the direction of the 

 axis of a rotating globe has much to do with the light which 

 different parts of it will receive from a luminous object. 



When the axis of the revolving globe was at right angles 

 to the line joining the globe and the light, no place on the 

 surface of the globe received light for a longer time than any 

 other place. This was not true when the axis was at any 

 other angle. 



