HEAT. V. 



17. The heat we receive from the sun. 



a. The heat varies with the time of day and 

 with the seasons. 



Experiment 21. The varying heat from 

 the sun. 



b. The heat varies with the color of the object 

 receiving it. (See Section 71.) 



Experiment 22. The effect of the sun's 

 heat upon different colors. 



c. The heat received by a large surface may be 



brought to a small surface, making it very 

 hot. 



Experiment 23. "The burning glass." 



18. Expansion due to heat. 



a. Examples of expansion. (See Section 72.) 



Experiment 24. Heat causes expansion. 



b. All materials do not expand the same 

 amount. 



Experiment 25. The results of unequal 

 expansion. 



19. The thermometer an application of expansion. 



Experiment 26. How to read a thermom- 

 eter. 



20. Heat produces light. 



a. The temperature of red heat and of white 

 heat. 



Experiment 27. Red-hot and white-hot. 



21. Heat from friction. 



a. The old way of making fire. 



Experiment 28. Primitive fire-making. 



