246 On the Cooling of Liquids in Vessels 



plunged into cold water, the difference in the rate of 

 cooling would be much greater. 



Hence we may conclude that teapots and coffee-pots 

 made of porcelain or earthenware and well gilded on 

 the outside would be not only as good, but even better 

 for common use than teapots and coffee-pots made of 

 silver. 



If equal quantities of warm water are placed in two 

 porcelain vessels of the same form and dimensions, and 

 with walls of the same thickness, the one gilded on the 

 outside, the other plain, and these vessels are allowed 

 at the same time to cool in still air, the gilded vessel is 

 found to cool more slowly than the plain one in the 

 proportion of 3 to 2, as has already been remarked; but 

 if, instead of allowing the vessels to cool in air which is 

 undisturbed, they are exposed to the action of a strong 

 and cold current of air, the difference in the rapidity of 

 cooling will be much less, as 6 to 5, for example; and 

 if the current of air is very strong, and at the same 

 time very cold, this difference will be still smaller. 



If, instead of exposing the vessels in the air, they are 

 plunged into cold water, the difference in the rapidity 

 with which they cool will be reduced to almost nothing. 



In the cases last mentioned we can say that the ex- 

 terior surfaces of both vessels, although of different 

 natures, yet, on being exposed to so great a degree of 

 cold, are cooled to such an extent as to be in a condition 

 to transmit the heat coming from the interior of the 

 vessel as fast as it can reach them after making its way 

 through the thickness of the walls, which offer all the 

 while a certain amount of resistance to its passage. 



To use another form of expression which I regard as 

 more exact, and consequently more suitable, especially 



