TEMPERATURE FACTS 205 



Using these hourly footings, find the average for the week by each 

 of the four methods. 



How do the averages compare? A little difference may be 

 expected. 



In different weeks and different seasons, slightly different results 

 may be obtained. 



Exercise 52. To Determine the Average Monthly Temperature 



At the end of the month compute the average temperature of the 

 month from the record kept by the class, using the maximum and 

 minimum method. Note the extremes for the month. Work out 

 also the prevailing wind direction for the month; the number of 

 clear, cloudy, and partly cloudy days; the* total rainfall, and the 

 depth of snowfall, if winter. 



III. TEMPERATURE FACTS ^ 



229. How the Atmosphere is Heated. Instead of being 

 warmed directly by the sun, the atmosphere receives most of 

 its heat indirectly. The sun warms the earth, and the air is 

 heated chiefly by contact with the warm earth and by heat 

 reflected from the earth into the air. For this reason the air 

 is nearly always warmest near the ground and grows colder 

 with elevation. 1 Recording thermometers sent up by kites or 

 small balloons over the Missouri valley have shown the 

 temperature at the height of a mile about 12 colder than at 

 the ground; at 5 miles 80 colder; at 10 miles 120 colder; 

 and at 20 miles about 93 colder than at the ground. These 

 figures change somewhat with the season. In the lower 2 or 3 

 miles of air many changes in temperature occur. 



230. Effect of Heat on the Atmosphere. This greater 

 heating of the air near the ground is one of the principal causes 

 of all movements of the atmosphere. Heating expands air 

 about J^Qi part of its volume for each added degree Fah- 

 renheit (show that this is ^73 for 1C.), which means that 

 warming air 50F. increases its volume about one-tenth. 



PROBLEM 



Show that, if the lower half-mile of the atmosphere is warmed 

 50F., the upper surface of the original half-mile would be raised 

 1 This is true up to 8 or 10 miles. 



