EXERCISE 13 



TO MAKE A CHART WHICH WILL SHOW GEAPHICALLY THE LENGTH OF DAY AND 



NIGHT AT VAKIOUS TIMES OF THE YEAR 



Materials. Cross-section paper ; a ruler ; an almanac giving time of sunrise and sunset through- 

 out the year. 



Directions. On the cross-section paper draw, in heavy black lines, as near as possible to the 

 center of the page, a rectangle 13 centimeters high and 12 centimeters wide. This should follow the 

 heavy centimeter lines. Let the vertical centimeter lines represent the even hours of the day from 

 midnight to midnight, and they should be so labeled. The horizontal centimeter lines, except the top 

 and bottom lines, will represent the first days of the twelve months. They should be labeled by 

 writing the names of the months to the left of the rectangle, opposite the proper lines. 



Find from an almanac the time of sunrise and sunset for the first day of each month, and mark 

 the points which will correspond to these hours on the proper month lines. Ink those portions of 

 the lines which represent night. When you have completed the chart examine it and state care- 

 fully what conclusions you may draw from it. 



Can you give a reason for the change of hours of sunshine and darkness ? 



Additional problem. What is the length of the longest and of the shortest periods of daylight at the 

 equator ? at the tropic of Cancer or of Capricorn ? at the arctic circle ? at one of the poles ? 



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