EXPANSION. 51 



heating ; air partially filling a bladder expands and fills 

 it by the operation of the same cause. 



108. HOW HEAT EXPANDS BODIES. - Heat 



How does heat 



operate to ex- operates to produce expansion, by insinua- 



pand bodies? tmg itsel f between the particles of Sllb- 



stances and increasing their distance from one another. 

 The cooling process is simply a removal of heat, 

 which allows the particles to assume their original dis- 

 tances from one another, in obedience to the attraction 

 of cohesion. 



109. EXPANSION OF SOLIDS. The ex- 



Among solids, . . 



which expand pansion of solids by heat is comparatively 

 the most? smalL Among S olids, the metals expand 

 the most ; but an iron wire increases only ^^2 in 

 length on being heated from zero up to 212. Ex- 

 pansion in general bulk is about three times as great 

 as in length. Thus, a cannon ball heated to 212 

 would occupy about zj-o niore space than when cooled 

 down to zero. 



110. ILLUSTRATION. The expansio-n of 



metals be U- "be lllustra- 

 lustrated ? , 



ted by ar- 



ranging a brick, a knit- 

 tirig-needle. and a shin- 

 gle, as in the figure. On 

 heating the needle with a spirit lamp, the shingle, if 

 before carefully poised, will be overturned. 

 What appli- 11L WHEEL-TIRES, RIVETS, ETC 



cation of this Important application of even this small 



expansion ts . . 



made in the degree of expansion is made in the arts. 

 t | reg Q carr j a g e w heels, for example, 



