SCIENCE OF COMMON THINGS. 149 



Linen cooler than cotton. Influence of heat on the soil. 



The air confined between the two surfaces of glass is 

 a non-conductor of heat, and equally opposes the escape 

 of caloric from within, or the penetration of cold air 

 from without. 



61 Why does a linen garment feel colder than a cotton one? 



Because linen is a much better conductor than cotton ; 

 and therefore (as soon as it touches the body) it draws 

 away the heat more rapidly, and produces a greater 

 sensation of cold. 



6S Why is the face cooled by wiping the temples with a fine cambric 

 handkerchief^ 



Because the fine fibres of the cambric have a strong 

 capillary attraction for moisture, and are excellent con- 

 ductors of heat ; in consequence of which the moisture 

 and heat are abstracted from the face by the cambric, 

 and a sensation of coolness produced. 



63 Why would not a cotton handkerchief do as well ? 



Because the coarse fibres of cotton have less capillary 

 attraction, and are very bad conductors; in conse- 

 quence of which the heat of the face would be increased 

 (rather than diminished^ by the use of a cotton hand- 

 kerchief. 



64 Is the soil a good conductor of heat f 



]N r o ; it is a very "bad conductor of heat. 



65 Why is the soil a bad conductor of heat ? 



Because its particles are not continuous; and the 

 power of conducting heat depends upon the density of 

 matter. 



966 Why is the soil (below the surface) warmer in winter than the sur- 

 face itself? 



Because it is a ~bad conductor of heat ; and therefore 

 (although the ground be frozen) the frost rarely pene* 

 trates more than a few inches below the surface. 



967* Why is the soil (below the surface) cooler in summer than the sur- 

 face itself 'f 



Because it is a bad conductor of heat ; and therefore 

 (although the surface be scorched with the burning sun) 



7* 



