26 H/STORr of the SOCIETr. 



mafles and temperatures are equal. But what Dr Hotton calls 

 fallacious and unphilofophical is, the afligning the change in 

 the capacity of a body for heat, as the caufe of the abforp- 

 tion or emiflion of heat, at the moment when that change 

 takes place. This fuppofition is grounded, as he contends, on 

 a falfe view of the fadls concerning the tranfition of water from 

 a hard to a fluid ftate, or the contrary. The chemifls, for 

 example, who maintain this do(5lrine, hold, that when water is 

 cooled down to a certain temperature, it neceflarily freezes and 

 becomes ice, a fubflance that has a much lefs capacity for heat 

 than water has ; on which account a certain quantity of the 

 heat contained in the water is expelled, and enters into the fur- 

 rounding bodies. Now in all this it is fuppofed, that water, at 

 a certain temperature, is neceflaril^j changed into ice, which is 

 by no means true ; becaufe it is well-known, that water rflay 

 be cooled feveral degrees below what is called the point of con- 

 gelation without lofmg its flmdity. Dr Hutton tells us, that he 

 has found means to cool it no lefs than 30° below that tempe- 

 rature, without its being changed into ice. Though it be true, 

 therefore, that water muft be cooled to a certain temperature 

 before it can freeze, it is not true, converfely, that it does freeze 

 whenever it is cooled to that temperature. It follows, as a ne- 

 ceflary confequence, that fomething elfe befide a change of tem- 

 perature is efltntial to congelation, and is the caufe of that won- 

 derful change which water undergoes in palling from a fluid to 

 a folid ftate. The feparation of the latent heat feems a caufe 

 more adequate to the effedl, and ferves to explain the cooling of 

 the water below the point of congelation, without the lofs of its 

 fluidity, becaufe this only happens when the efcape of the la- 

 tent heat is prevented. 



That the heat, abforbed by the water, is the true caufe of 

 its fluidity, appears from tlie facility with which this hypothelis 



explains 



