and the rate of evaporation? Whenever a liquid is changed to a vapor, heat is required. In 

 this case the heat is taken from the hand, thus causing it to feel cool, (d) Following this 

 line of reasoning, explain why people sweat. 



16. On the supply table you will find two cups of soil.* The soil is the same in both 

 cups except that one is moist while the other is dry. (a) Compare the readings of the 

 thermometers which record the temperature of the soils in these cups. Record the number 

 of degrees difference, (b) Infer the cause for this difference in temperature, (c) Under 

 similar conditions which kind of soil will "warm up" more easily, soil which is relatively dry 

 or soil which contains a relatively large amount of water? Explain at least in part. 



17. (a) What difference have you» observed between light and dark colored clothing as 

 to comfort in hot sunshine? (b) How do you explain the difference observed? 



18. Fill two shallow pans with silt. Sprinkle a little lime over the surface of one and 

 a little lamp black or powdered charcoal over the other. Place thermometers in position to 

 record the surface temperature of the contents of the pans. (The thermometer bulbs should 

 be placed just below the surface of the silt.) (a) Before placing the apparatus in direct sun- 

 light, allow it to stand for a few minutes and then take the readings of the thermometers. 

 As soon as you have taken the initial readings, place the apparatus in direct sunlight, (b) 

 After a few minutes record the readings again, (c) Calculate any difference in the readings 

 recorded, (d) Infer a reason for any difference in temperature. 



19. Hold your hand in such a position in direct sunlight that the sun's rays will strike 

 the palm very obliquely. After holding it in this position for a time, turn the hand so that 

 the sun's rays will strike the palm vertically, (a) Notice any change in heat sensation, (b) 

 Recall any evidence of the difference in temperature on the north and south side of a roof, 

 (c) Infer concerning the difference in temperature between the north and south slopes of 

 hills in a rolling country. 



20. State three conditions which will affect soil temperatures. 



•The soil in one cup should have been moistened at least an hour before reading its temperature. 



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