TELLING TIME BY THE SUN 13 



a. Draw a circle on a board using the protractor, 

 and divide it into 24 equal 

 parts. How many de- 

 grees are there in each 

 part? Drive a nail into 

 its center so that it makes 

 an angle of 90 with the 

 board, in all directions. 

 You can do this by hold- 

 i n g your protractor 

 against the nail as you 

 drive it. Draw a line from 

 the nail lengthwise of the board and place the board so 

 that this line runs north and south. How can you do this? 

 Mark this line 12, where it crosses the circle on the 

 north side, and then mark the other divisions properly 

 Is there any need to mark all of the divisions? Why? 

 What time does the shadow tell in the illustration? 



8. Other Ways of Telling Time. 



The sundial is a good way of telling time on sunny 

 days, but if we w r ant to know the time when the sun is 

 not shining we must use other methods. Long ago the 

 sand-glass, or hour-glass was invented to tell the length, 

 of an hour. This was made by connecting two bulbs or 

 globes by means of a small tube and having one glob^ 

 filled with sand. The filled globe was placed on top and 

 the sand slipped slowly through the small hole into the 

 lower globe. When all the sand had left the upper globe 

 an hour had passed. Then the hour-glass was turned up- 

 side down and a record was kept of the number of hours. 

 Why was the name hour-glass given? 



