94 GENERAL SCIENCE 



19. Why do we have an oppressive night after a muggy day? 



20. Why is the bottom of a teakettle rough and black? 



21. What should the sides of a teakettle be like? Why? 



22. Why are furnace pipes polished? 



23. What is the advantage and the disadvantage of a highly 

 polished stove. 



24. How does the glass in a hothouse act as a trap to catch heat? 



25. Does the heat of the sun come through the window? 



26. Why are the tops of mountains so cold although nearer the 

 sun than the valleys? 



27. Why will a slight covering over plants prevent frost? 



28. Why is there no frost on a cloudy night? 



29. How do we get the greater part of our heat from a fireplace? 

 Why is not the fireplace as economical as a stove? 



30. Why are the connecting pipes of a boiler polished? 



31. Why is china glazed? 



32. Why may flowers be raised under glass out-of-doors during 

 the winter? 



33. Why does the snow melt at the foot of a tree more quickly 

 than in the open field? 



CONDUCTION 



Difference between Conduction and Convection. There are 

 two other ways by which heat is transmitted: conduction, which 

 is to be studied in this section, and convection, which is to be studied 

 in the next section. 



To get a clear idea of the difference between the two methods, 

 pass a book from one student to another along the class. The 

 book is conducted or passed from pupil to pupil. Heat travels in 

 the same manner. The heat is given from one particle or mole- 

 cule to another of an iron bar, one end of which is in a flame, and 

 the other end in your hand. In this way the heat is conducted to 

 your hand. The heat has traveled by conduction. 



If one of the pupils carries the book from one end of the class 

 to the other, we may call this method of getting the book from one 

 place to another convection. Most solids transmit heat by con- 

 duction, while liquids and gases transmit heat by convection. Air 



