182 LABORATORY LESSONS 'IN GENERAL SCIENCE 



wire axis reach up through and above it. Turn the sphere 

 together with this cardboard horizon on the wire as an axis, 

 i.e., rotate the sphere. Note that the east horizon (front 

 edge) falls lower and lower below objects which were at first 

 out of sight of an observer as located by the tack, thus 

 causing them to "rise." Note, too, that the opposite (west) 

 horizon of the cardboard passes objects and shuts them from 

 view, causing them to "set" for the same observer. 



Explain (a) how this exhibits succession of daytime and 

 nighttime on the earth; (b) how it is that when we have 

 nighttime, and can see the stars^ there are people elsewhere 

 in the world who are having daytime. 



7. With the sphere and a lighted candle, but without the 

 cardboard, note how by turning the sphere on its axis the 

 marked place of the observer's position comes around on 

 the side where the light is, then passes through the region 

 of illumination (daytime), and then on for a period (night- 

 time) when the light cannot be seen. 



Repeating such rotation, state when for the observer on 

 the earth there occurs (a) sunrise ; (b) noonday ; (c) sunset. 

 State (a) how often these occur; (b) when a day's period 

 is completed. Why is the sun not seen at all times ? 



8. Define for a rotating body (a) axis; (6) poles; (c) 

 equator ; (d) parallels of latitude. 



9. Repeat paragraph 7, holding the sphere so that the 

 illumination reaches from pole to pole. State where a line 

 drawn from the source of light to the center of the sphere 

 cuts the surface of the sphere. Letting the light represent 

 the sun and the sphere the earth, state where on the earth 



