22 



A YEAR IN SCIENCE 



with sawdust, asbestos, excelsior, or some other poor 

 conducting material. Foods are heated to a high 

 temperature and then placed in the inner vessel. This 

 heat remains in the food, and slowly cooks it, because 

 the non-conducting material prevents the heat from 

 escaping. 

 Explanation of conduction. When a body is heated 



the molecules in the part in contact with the heat move 



s 



Cork 



Fig. 12. Section of a fireless cooker ; s } soapstone ; k, kettle. 



more rapidly. In their movement they strike harder 

 and faster upon those next to them, so that these in 

 turn move as rapidly as the first ones. In this way the 

 motion is carried from one group of molecules to 

 another. 



Convection. Notwithstanding the fact that air and 



