and the Mode of its Communication. 83 



inches in diameter, was placed on each of the platters, 

 and served as a perforated cover to it. 



The stands on which the platters were supported 

 were of such a height that the upper surface of the flat 

 bottom of each of the platters was elevated just 40 

 inches above the level of the floor of the room ; and 

 the horizontal arms of the wooden stand which sup- 

 ported the conical vessels were of such a height that 

 the flat bottoms of these vessels (which were placed per- 

 pendicularly over the centres of the platters) were just 

 4 inches above the flat horizontal surface of the bottoms 

 of the platters. 



One of the platters was at the temperature of the air 

 of the room (63 F.), but the other was kept constantly 

 ice-cold, during the whole of the time the experiment 

 lasted, by means of pounded ice and water, which was 

 put into the earthen dish, over which, or rather in 

 which, this platter was placed. 



Each of the platters was just I inch deep, measured 

 from the level of the top of its brim to the level of the 

 upper surface of the flat part of its bottom ; this flat 

 part was about 8 inches in diameter. 



The wo conical vessels were now filled with boiling- 

 hot water, and the times of their cooling were carefully 

 observed. 



From the above description of the apparatus used in 

 this experiment, it is evident that the vessel which was 

 suspended over the ice could not be reached by any 

 streams of cold air that might be occasioned by that ice, 

 or by the cooled sides of the vessel which contained 

 it ; for the air which, coming into contact with the sides 

 of that vessel, was cooled by it, becoming specifically 

 heavier than it was before, naturally descended, and 



