242 On the Cooling of Liquids in Vessels 



In order to throw light on this subject, which had sev- 

 eral points of interest for me, I made the following 

 experiment. I procured (from M. Nast, a celebrated 

 porcelain manufacturer, of Paris) two vessels of porce- 

 lain, of the same shape and of the same dimensions, 

 the one white, the other completely covered on the out- 

 side with gilding; into these vessels I put equal quan- 

 tities (250 grammes, or a quarter of a litre) of warm 

 water, and then allowed them to cool gradually in a 

 large room free from currents of air, having placed them 

 three feet apart on a table in the middle of the room. 



Each of the vessels was closed with a cork stopper, 

 and by means of a mercurial thermometer with a cylin- 

 drical bulb, fixed in the axis of the vessel in such a way 

 that while the thermometer was inserted in the cork the 

 scale remained on the outside of the vessel, I noted 

 very conveniently the progress of the cooling without 

 touching the vessel, and without even approaching it 

 sufficiently near for the heat of my body to interfere 

 sensibly with the operation of cooling. 



The result of this experiment was as I had expected. 

 The gilded vessel cooled much more slowly than the 

 plain one. Starting at the same time with both vessels 

 at the same temperature, if it took half an hour for the 

 plain vessel to cool down through a certain number of 

 degrees, three quarters of an hour were necessary for the 

 gilded one to cool down to the same point. 



This comparative experiment was repeated several 

 times, and invariably with the same result ; the gilded 

 vessel always cooled more slowly than the plain one in 

 about the proportion of 3 to 2. 



The advantage that can be gained from this remarka- 

 ble property, possessed by metallic surfaces, of resisting 



