ATMOSPHERIC TEMPERATURES 131 



acts as a blanket to the earth and keeps in the heat of the 

 sun just as blankets on a bed keep in the heat of the body. 

 If there were no atmosphere on the earth, its surface would 

 become intensely hot during the day, when the sun shines 

 directly upon it, and intensely cold at night, so that it 

 would not be possible for life to exist. 



It has been estimated that, if there were no atmosphere, 

 the mean temperature of the earth's surface during the 

 day would be 350 F. and during the night - 123 F. 

 Thus the atmosphere is not only needed for the breathing 

 of plants and animals and for carrying moisture, but also 

 for keeping in the heat of the sun. On the moon, where 

 there is no atmosphere, there can be no life as we know it. 



65. Cause of the Variation in Atmospheric Temperatures. 

 Experiment 76. Cut a hole 4 in. square in the center of a board 12 

 in. square. Fit tightly into this hole one end of a wooden tube 4 in. 



Fig. 64. 



square and 1 ft. long. Paint the inside and outside of the tube a dull 

 black. Hinge the opposite end of this tube 10 in. from the end of a 

 baseboard 2 ft. long and 16 in. wide, having 6 in. of the board on 

 either side of the tube. 



On a clear day place this apparatus out of doors on a table freely 

 exposed to the sun with a piece of paper on the baseboard under the 

 end of the tube. Point the tube directly at the sun in the early 

 morning, in the middle of the forenoon, at noon, in the middle of the 

 afternoon and about sunset. Mark on the paper the amount of sur- 

 face illuminated by the sunlight passing through the tube at each of 



