12 THE SUN, STARS, AND PLANKTS 



3. How can you tell the direction of sunrise by 

 knowing the direction of sunset? 



4. On what days does the sun rise at six o'clock 

 and set at six o'clock? 



5. How can you tell when it is noon by a shadow? 



6. How can you tell where the north is by a shadow? 



7. If the sun sets S. 85 W. where does it rise? 

 Make a drawing of this, using the protractor, and obtain 

 your answer from the drawing. 



8. If the sun sets N. 80 W. where does it rise? 

 Make a drawing as in the previous question. 



7. Telling Time by the Sun. 



In olden times, before clocks were made, people 

 used to tell time by the sun. Even now there are many 

 persons who can judge the time very nearly, by the posi- 

 tion of the sun in the sky. Yet it is impossible to learn 

 the time from the sun, with exactness, unless we make 

 use of a simple piece of apparatus. Just a stick driven 

 into the ground is all that is necessary. When the 

 shadow points north it is noon. See Experiment 3. 

 When the shadows cast at sunrise and sunset are oppo- 

 site each other the time of each is six o'clock. If the 

 semi-circle on the north side of the stick is divided into 

 twelve equal parts, the shadow will take one hour to pass 

 over each part. These divisions may be marked with 

 the hours between six in the morning and six at night. 

 Over how many degrees does the shadow move in one 

 hour? 



Experiment 7. The Sundial. 

 Apparatus: Board, protractor, nail. 



