ON THE EFFECTS OF HEAT. 101 



collecting, that motion is facilitated by the addition of 

 caloric. Elasticity is caused by the compression of the at- Elasticity. 

 mospheres, and their return to their former state. 



There is another phenomenon, which I bejieve no one Expansion of 

 has ever attempted to explain, I mean, the expansion of dimmutitTn of 

 water by a diminution of temperature. We will suppose, temperature, 

 ■with Mr. Dalton,'that water is at its maximum of density 

 at 36*. Its expansion by heat requires no explanation. 

 Let us see how far its expansion by cold may be accounted 

 for. It must be granted, that ice has a less affinity for calo- 

 ric than water has, otherwise water would not give out 

 caloric at the moment of its becoming solid. Hence it 

 follows, that, when water is cooled, it must at last reach 

 some point, at which its affinity for caloric will diminish. 

 In most substances this probably does not happen till they 

 reach the point of congelation : but when water is cooled 

 below 36°, its affinity for caloric begins to diminish ; the at- 

 mospheres, therefore, which surround its particles (and of 

 course the water itself) will expand. Although the particles 

 are nearest to each oiher at 36°, their attraction is not them 

 sufficient to overcome the resistance of their atmospheres: 

 these therefore will continue to expand, until they are so far 

 rarefied as not to be able to resist the affinity of the particles 

 for each other. But this will not happen till the water is 

 cooled many degrees below the freezing point, unless by 

 agitation, or some other means, they are brought nearer 

 into contact. 



It was before stated, that the density of the atmospheres Its expansion 

 was the cause of solidity : but the specific gravity of ice is °" solidifica. 

 1 1 1 . r . ' ^ • , , . , lio" owing to 



less than that ot water ; it also contains less caloric ; hence crystallization 



its atmospheres must be less dense; it oueht, therefore, ^V^ "^f *^^^® 



1 « • 1 1 1 • 1 • 1 ^ w'^ other 



to be more fluid than water, which is not the tact. How bodies. 



is this anomaly to be explained ? It must be remembered, 

 that not only ice, but all solutions of salts, &c., which form 

 prismatic crystals, undergo the same expansion, during their 

 transition from the fluid to the solid state. It is pro- ^ 



bably the tendency, which the particles of these bodies 

 have to arrange themselves in prismatic forms, that causes 

 this expansion : and the diminution of specific gravity may 

 be occasioned by interstices between the prisms. In addi- 

 tion 



