RADIATION OF HEAT 27 



called radiators, which are intended to give large surface so 

 that the heat of the water may be readily given up to the air 

 of the room. It will be noted that no fresh air is supplied by 

 this method of heating, and therefore some ventilation is 

 necessary. The advantage of this system is that all of the 

 house may be evenly heated whether the wind blows or not. 

 See Section 190, Dangers of Vitiated Air. 



Heating by means of steam will be explained in Section 25, 

 Evaporation and Condensation. 



References : 



1. 1710 : 33-45. Heating and Ventilation. 



2. 1803 : 223-225. Heating and Ventilation. 

 a. 1801 : 290. Ventilation. 



6. 1804:298-302. Ventilation. 



c. 1805 : 326. Ventilation. 



d. 1808 : 218. Ventilatkm. 



e. 1809 : 161. Ventilation. 



20. RADIATION OF HEAT 



Heat is also radiated ; that is, it passes off in straight lines 

 from one body to all other bodies. In some way the swiftly 

 moving molecules have the power to give out energy very 

 similar to, though much weaker than, the energy we receive 

 from the sun. Radiated heat is very noticeable if we are in 

 front of an open fireplace, for the radiation there is caused 

 only from the action of molecules. The energy from the sun 

 may be condensed by means of a lens or " burning glass " 

 and so high a temperature obtained as to set fire to paper, 

 cloth, and even wood and coal. 



Material which is black and rough is the best radiator; 

 that which is smooth and shiny makes a very poor radiator, 

 therefore if we wish to keep anything hot, we should place it 



