of WJrER hy HEAT. 403 



When heat caufes expanfion, it is imagined to a(fl by indu- 

 cing a repulfion among the particles of bodies, which, oppofmg 

 and overpowering the cohefive attradion, caufes the particles to 

 recede. 



In what manner, then, the addition of heat can occafion, or 

 allow, the particles of water to approach each other, and how 

 the fubtracflion of it can make them retire to a greater diftance, 

 I confefs I can in no meafure comprehend. 



An explanation, abundantly plaufible at firft view, very rea- 

 dily fuggefts itfelf to every one who is aware of the great and 

 forcible expanfion which happens to this fluid at the moment of 

 its congelation. It is ftated by Sir Charles Blagden, in the 

 paper already quoted. 



The remarkable dilatation which water experiences at the 

 infkant of being converted into ice, is very generally afcribed, 

 and I prefume very properly, to a new arrangement which the 

 particles aflfume, determined probably by their polarity ; by 

 which one fide of the particle A is attra(5live of one fide of B, 

 while it is repulfive of another. 



Now, if this polarity operates with fb much energy as to im- 

 part almoft irrefiftible expanfive force at temperature 32°, it is 

 reafonable to fuppofe that it may begin to exert its influence, 

 though in a far inferior degree, at temperatures fomewhat more 

 elevated. The expanfion, therefore, that takes place, during the 

 fall of temperature from 40°, may be imputed to the particles 

 beginning or afiedting to aflfume that new arrangement which 

 their polarity afl!igns them, in which arrangement thefe particles 

 occupy more fpace than before. 



Again, when heat caufes water of 32° to contradl, upon the 

 fame principle, it may be conceived to operate, by countera(5ting 

 the fmall portion of the difpofition to polarity that furvives the 

 llquefa<5lion. 



I 



