98 



Introduction to the Study of Science 



Make a diagram illustrating the facts of air circulation in the 



room. 



Heating buildings by means of " hot-air " furnaces (Fig. 30) depends 



upon this manner of heat transfer. Make a plan of a furnace and dis- 



tributing pipes, and cold air supply. Show the course of the air from 

 its reception by the cold-air box to its delivery in 

 different parts of the building. Explain what takes 

 place as the air comes into contact with the hot 

 furnace. Why does it move through the distrib- 

 uting pipes and not out through the cold-air box? 

 If the hot air from the registers fails to reach all 

 parts of the room, will the temperature in all parts 

 of the room be the same? 



Liquids, which as you know are poor con- 

 ductors, distribute heat in the same way as air. 

 Portions being heated lose density and are 

 forced away from the heat source by the 

 denser portions. You may readily demon- 

 strate the fact by applying heat to the bottom 

 only of a test tube full of cold water. Ob- 

 serve the way in which the heated portions 

 of the water are transferred from bottom to 

 top. Are there currents downward as well as 

 pie representation upwarc j? Try this out by applying heat to 



ol & xiotr"W&<tiGr sys- m 1111* * i 



tem. Identify the the top of water in a test tube, holding the 



warm and the cold lower t Q f the tube in the hand T h e 



water currents. 



Explain transfer of course of the heated parts of water will be 



warm water from d Conspicuous if some Small parti- 



lower bottle to the 



upper, is any of cles of coloring material, as aniline dye, are 



t mto th bottom of the tube. 



FIG. 31. Sim- 



the water in the 

 upper bottle heated 

 by conduction? 

 Explain your an- 

 swer. 



Exercise : Convection currents in water. The 

 important fact may be illustrated clearly by either 

 of the following demonstrations. Set up the ap- 

 paratus shown in Fig. 31. Put some coloring matter in the bottle 

 or lamp chimney to show the course of circulation. The chimney may 

 be taken to represent the hot-water tank ; the glass tubing to repre- 

 sent the pipes connecting the tank with the water coil in the range 



