122 



THE PRODUCTION AND USE OF HEAT 



2. Radiation takes place through a vacuum as well as through 

 air. 



3. The rate of radiation varies with the temperature of the 

 heated body. 



It is known that the amount of heat given off from the stove 

 by radiation as compared to that given off by convection 

 currents is dependent upon the temperature of the stove. 

 The higher the temperature, the greater the proportion of 

 heat given off by radiation. It is probable, though, that in 

 the case of the ordinary stove one-fourth to one-third of 

 the heat is given off as radiant heat and the remainder in 

 the convection currents. 



140. Jacketing the Schoolroom Stove. It is difficult to 

 heat schoolrooms properly by means of stoves. The room is 

 usually allowed to get cold at night. In severe weather the 

 room is often uncomfortably cold when the opening hour 

 arrives. In an endeavor to heat the room, the janitor has 



the stove heated to a high temper- 

 ature. The result is that a much 

 larger portion of the heat than 

 usual is being given off as radiant 

 heat. The pupils and furniture 

 near the stove are consequently 

 overheated, while the pupils at the 

 outer edges of the room are suffer- 

 ing with the cold. 



The remedy for this defect is 

 found in placing a sheet-iron jacket 

 around the stove (Fig. 90). The 



jacket should be 4 or 5 ft. in diameter and have a door in 

 front through which the stove may be reached. It should 

 be supported 6 or 8 in. from the floor and should reach to 

 the top of the stove. This jacket catches most of the radiant 

 heat. The cool air comes into contact with it and is heated 

 as it is by the stove. The jacket not only prevents the 

 overheating of Jbhe portion of the room nearest the stove by 



FIG. 90. A jacketed stove. 



