228 WELLS'S NATURAL PHILOSOPHY. 



Is the form of 520. The form of all bodies appears to be 

 pendcur'upon entirely dependent on heat ; by its increase 

 *'^" solids are converted into liquids, and liquids 



into vapor ; by its diminution vapors are condensed into 

 liquids, and these in turn become solids. 



If matter ceased to be influenced by heat, all liquids, vapors, and doubtless 

 even gases, would become permanently solid, and all motion on the surface of 

 the earth would be arrested. 



What are the ^^1. Tho tln'ce most apparent effects of 

 J)arent°°effects ^^^at, SO far as relate to the form and dimen- 

 ofheat? sions of bodics, are Expansion, Liquefaction, 



and Vaporization. 



Heat operates to produce expansion by introducing a repulsive force among 

 the particles of the body it pervades. This repulsive force, in the case of 

 solids, weakens or overcomes the attraction of cohesion, and gives to the par- 

 ticles of all matter a tendency to separate, or increase their distance from one 

 another. Hence the general mass of the body is made to occupy a larger 

 space, or expand. 



In what bodies ^^2, The cxpausion occasioned by heat is 

 ducethe^'^maN g^eatcst lu thosc bodies which are the least in- 

 est expansion? fl^enced by the attraction of cohesion. Thus 

 the expansion of solids is comparatively triflinj^, that 

 of liquids much greater, and that of gases very consid- 

 erable. 



Do bodies con- 523. Thc expausion of the same body will 

 "rnd as° lo^^n " coutinue to iucreasc with the quantity of heat 

 as heat enters ^\^^ entcrs it, SO loug as the form and chemi- 



tuem I . 



cal constitution of the body is preserved. 

 524. Among solids the metals expand the most ; but 

 an iron wire increases only 1-282 in bulk when heated from 

 32° of the thermometer up to 212. 



Solids appear to expand uniformly from the freezing point of water up to 

 212°, tlie boiling point of water ; — that is to say, the increase of volume which 

 attends each degree of temperature which the body receives is equal. When 

 solids are elevated, however, to temperatures above 212°, they do not dilate 

 uniformly, but expand in an increasing ratio. 



The expansion of solids by heat is clearly shown by the following experi- 

 ment, Fig. 202 : m represents a ring of metal, through which, at the ordinary 

 temperature, a small iron or copper ball, a, will pass freely, this ball being a 

 little less than the diameter of the ring. If this ball be now heated by the 



