HISTORY of the SO CI Err. 37 



explains ail the other phenomena of congelation. There is, as 

 has juft been faid, a certain fixed temperature, at which water 

 and ice are convertible into one another. At this temperature, 

 however, a mixed body of ice and water may remain for ever 

 without any of the water being congealed, or any of the ice 

 melted ; but let there be added to t^is compound mafs a quan- 

 tity of heat, by communication from a warm body, and there 

 is a certain quantity of the ice melted, while the mafs remains in 

 its former temperature. Now, if we meafure the quantity of 

 the heat, communicated to this compound mafs, without chan- 

 ging its temperature, and alfo the quantity of ice melted, that is, 

 the quantity of fluidity produced, it will be found that they are 

 in all cafes proportional to one another, and have therefore 

 the relation of caufe and efFedt. This certainly amounts to no 

 lefs than a full demonftration, that the heat abforbed, or ren- 

 dered infenfible to the thermometer, is the caufe of fluidity. 

 To fay, that the change of the capacity for heat is the caufe of 

 the abforption of the heat, is, in fadl, to afErm, that the fluidity 

 of the water is the caufe of that abforption, and, of confequence, 

 leaves the fluidity as a phenomenon without a caufe : for it has 

 been fliown that mere change of temperatu.re is not the caufe 

 of it. 



Dr Hutton has been remarkably happy in his explanation 

 of the manner in which heat pi-oduces fluidity. Heat, fays he, 

 has two diftindl effedls on body : The one of thefe confifts in 

 its power of difliending the fubftance of the body, or increafing 

 its volume, and this is the effeA that is meafured diredly by 

 the thermometer : The other efie<fl of heat is to move the par- 

 ticles of hard bodies on their axes, and by this rotatory mo- 

 tion to feparate their poles of attraction, which were united 

 in their /late of hardnefs and folidity. The particles of the 

 body, in confequence of this rotatory motion, are in a flate 



c 2 of 



