42 HEAT 



and thus become very warm. What color of clothing 

 should be worn in hot weather? Why? 



Experiment 22. The Amount of Heat Received by 

 Different Colors. 



Apparatus: Two spice cans of the same size, kero- 

 sene lamp, pieces of paper, white, red, yellow, and black. 



a. Polish one spice can and smoke the other in the 

 flame of a kerosene lamp. Fill each with the same amount 

 of water and expose both in the bright sunshine. At 

 the end of twenty minutes dip a finger into each and tell 

 what the difference is between them. See Section 71. 



b. While waiting for the water to become warm 

 expose the pieces of paper to the bright sunshine and 

 arrange them in the order of their warmth, putting the 

 hottest one first and the coldest one last. 



We have seen that the amount of heat from sunshine 

 varies with the altitude of the sun, because when the sun 

 is low a given amount of sunshine is spread over a much 

 greater surface than when the sun is higher. Do you 

 think that if we could cause more sunshine to fall upon 

 a certain surface it would become warmer? See Experi- 

 ment 17. 



There is another means by which light and heat 

 may be gathered together so that what falls upon a large 

 surface is caused to cover only a very small surface. 

 This is accomplished by the use of a circular shaped 

 piece of glass, thicker at the center than at the edges, 

 called a lens, or "burning glass." 



