184 LABORATORY LESSONS IN GENERAL SCIENCE 



(a) Where vertical rays from the sun (direction from center 

 to center of spheres) fall on the earth relative to its equator. 



(6) What circles on 

 the earth are marked 

 I out by these vertical 

 rays, and by those 

 rays reaching farthest 

 north and farthest 

 south, as the earth 



FIG. 80. December 21st. j s ma de to rotate ? 



3. Move the sphere representing the earth a quarter way 

 round the cardboard to the right (as one faces the center), 

 observing all the re- 

 quirements of I and II 



in paragraph 1 above. 

 State what is now noted 

 as required in (a) and 

 (6) of paragraph 2. 



4. Move the sphere 

 to the other end of the 



. . FIG. 81. March 21st, and September 22d. 



major axis, and farthest 



from the marble. State as in paragraph 2, (a) and (6). 



5. Move the sphere on to three quarters of the way 

 around the cardboard, and state as above. 



6. When a complete revolution of the earth about the sun 

 is accomplished, what period of time has elapsed? In the 

 northern hemisphere, what season of the year is represented 

 by each of the four positions of the sphere? 



7. State in detail why these changes in the position of 

 the earth in its orbit cause changes of seasons for us, 



