100 



GENERAL SCIENCE 



30. Why will mist clear from lenses surrounded with gold rims 

 more quickly than from rimless glasses? 



CONVECTION 



Conduction and Convection as Applied to our Clothing. Air 

 which cannot circulate and carry heat by convection is one of the 



best heat insulators to be 

 found. Cotton, wool, 

 feathers, cork, etc., are 

 good insulators because 

 they contain a large 

 amount of air in the cells 

 or in the spaces between 

 the fibers. Clothing keeps 

 in the heat of the body 

 chiefly because it contains 

 air between the layers 

 and in the meshes of the 

 cloth. When the enclosed 

 warm air is displaced and 

 is replaced by colder air, 

 as is the case in windy 

 weather, the clothing no 

 longer keeps one so warm. 

 If clothing is closely fit- 

 ting, there is less room for 

 an air layer between the 

 layers of clothing, and, 

 therefore, it is less warm. 

 To keep one warm in cold, 

 windy weather the clothing 

 should consist of loosely- 

 fitting garments, prefer- 

 ably of wool, with some 

 outside wrap which is 



nearly wind proof, such as very closely woven cloth, or even leather 

 or rubber. A fur coat is very much warmer if the fur is on the 



FIG. 78. 



