no "Pfanmena exhibited by Bodies in [Book II. 



ways remains fluid or folid. There are, it is true, 

 fbnje bodies which appear in an intermediate ilate of 

 fluidity, fuch as wax, tallow, &c. j yet even in thefe 

 the point at which they become fluid is a fettled point, 

 though the different flages of foftnefs depend upon the 

 degrees of heat. 



In expanfion alfo the fenfible heat is increafcd in 

 proportion to the effect ; but it is different in fluidity j 

 for when bodies are arrived at the melting point, or 

 point of fluidity, a large, quantity of elementary fire is 

 abforbed, without producing any fenfible heat, or al- 

 tering the temperature of the body. This abibrption 

 of the matter of fire frequently continues a confider- 

 able time, according to the fupply from the adjacent 

 bodies. Thus, when a thaw comes on, the heat is 

 often far above the freezing point; and though 

 the ice melts flowly, it is conftantly furrounded by 

 air warmer than itfelf, and conftaatly imbibing the 

 matter of fire from it. On the other hand, if a quan- 

 tity of boiling water is thrown upon ice, it will im- 

 mediately melt : which proves that there is no diffi- 

 culty in feparating the particles of ice, if a fufficient 

 quantity of heat is fupplied : but the reafon of thefc 

 facts will be rendered clearer by the following expe- 

 riments. 



If a pound of water at 32 is mixed with an equal 

 quantity of that fluid at 172, the temperature of the 

 mixture will be 102, which is the arithmetical mean 

 between the heat of the two fluids ; but if a pound of 

 ice at 32 is mixed with a pound of water at 172", the 

 temperature of the mixture will be 32. Hence it 

 appears, that in the melting of the ice one hundred 

 and forty degrees of heat (that is, fuclva quantity of 

 elementary fire as is necefTary to excite that degree 

 8 of 



