THE B'EASON WHY. 49 



"The earth is the Lori's, and the fulness thereof; the world, and they that 

 ^ dwell therein." PSALM xxrv. 



136. What does the hearth-stone do with the heat tJiat it 

 receives ? 



It delivers it to the surrounding air, and to any other bodies 

 with which it may be in contact and as it parts with heat, it takes 

 up more from any body hotter than itself. 



137. When there is no fire in a room, what is the rela- 

 tive temperature of the various things in the room ? 



They are all of the same temperature. 



138. If all the articles in the room are of the same tem- 

 perature, why do some feel colder than others ? 



Because they differ in their relative powers of conduction. Those 

 that are the best conductors feel coldest, as they convey away the 

 heat of the hand most rapidly. 



[If you lay your hand upon the woollen table cover, or upon the sleeve of your 

 coat or mantle, it will feel neither warm nor cold, under ordinary circum- 

 stances. But if you raise your hand from the table cover, or coat, and lay it on 

 the marble mantel- piece, the mantel-piece will feel cold. If now you return 

 your hand from the inantel-piece to the table cover or coat, a sensation of 

 viarmth will become distinctly perceptible. This will afford a good conception 

 of the relative powers of conduction of wool and marble.'} 



139. Sow long does a substance feel cold or hot to the 

 touch ? 



Until it has brought the part touching it to the same temperature 

 as itself. 



140. When do substances feel neither hot nor cold ? 

 When they are of the same temperature as our bodies. 



141. Why, under these circumstances, do they feel neither 

 hot nor cold ? 



Because they neither take heat from, nor supply it to, the 

 body. 



142. Wliich would feel the warmer, when the fire wot 

 lighted, the Tiearth-rug or the hearth-stone ? 



The hearth-stone, because it is a good conductor, and would not 

 only fmwtu heat readily, but would fart with it as freely (thereby 

 3 



