135 
and the Mode of its Communication . 
This being done, I suspended these two vessels, in an erect 
position, or with their bottoms downwards, to the two opposite 
horizontal arms of a wooden stand, provided for the experiment; 
and I placed under each of them a pewter platter, blackened on 
the inside, by holding it over a lighted wax candle. 
Each of these platters "was 12 inches in diameter; and they 
were supported on the top of two shallow earthen dishes, each 
of which was 1 1 \ inches in diameter at its brim ; these earthen 
dishes being supported on circular wooden stands, 10 inches in 
diameter. 
A circular piece of thick drawing-paper, 12^ inches in dia- 
meter, with a circular hole in its centre, just 6 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 supported the conical vessels, was 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 1 inch deep, measured from the 
level of the top of its brim to the level of the upper surface of 
