HEAT. 



13 



explain the expansion of water in freez- 

 ing : the most plausible of which is, 

 that given by De Mairan, who supposed 

 that the particles when they crystallize 

 and assume the solid state, have a ten- 

 dency to unite by certain sides in pre- 

 ference to others, arranging themselves 

 so as to form right lines at determi- 

 nate angles. This arrangement of the 

 particles requiring more space, and 

 leaving numerous vacuities, the bulk 

 of the whole must necessarily be en- 

 larged. 



The most important effects result from 

 the remarkable property of water which 

 has been described. If the density of 

 water continued to decrease until it ar- 

 rived at the freezing point, ice would be 

 heavier than water, and as soon as 

 formed would subside to the bottom in 

 successive flakes, until the whole of the 

 water, however deep, should become 

 solid. The effects of such an arrange- 

 ment can easily be conceived. Climates 

 which, according to the present state of 

 things, are the delightful abodes of in- 

 numerable animated beings, would be 

 rendered unfavourable to their existence, 

 and must inevitably become dreaiy and 

 desolate. On the contrary, since water 

 expands previously to its freezing, ice is 

 lighter than water, and floats upon its 

 surface, protecting the water below from 

 the influence of frost. 



Aeriform bodies in their expansion 

 differ from solids and fluids, in being 

 uniformly affected by the same quan- 

 tities of heat applied to them at all tem- 

 peratures, which is thus explained. The 

 attractive force that exists in solids and 

 fluids resisting the expansive effect of 

 heat, the first portions applied have 

 most of this resistance opposed to them, 

 and therefore produce less expansion 

 than succeeding portions, which have 

 less resistance to contend with ; but as 

 there is no cohesive attraction existing 

 among the particles of aeriform bodies, 

 there is no resistance opposed to the 

 expansive power of heat upon them ; 

 and consequently all of them undergo 

 the same degrees of expansion with the 

 same degrees of heat ; and the same 

 effect is produced upon all of them by 

 equal quantities of heat applied at all 

 different temperatures. 



The following 1 TABLE gives the changes 

 of bulk produced upon 100,000 parts of 

 air, by every additional degree of Fahr- 

 enheit, from 32 to 100; and by every 

 additional ten degrees afterwards to 

 210. 



(& JUO,0*U 



Ex. The expansion of air may be 

 pleasingly illustrated by a simple appa- 

 ratus, such as is shown vA.fig.4. 



fid- 4. 



