127 
Sir H. Davy on the formation of mists. 
river or lake, when the temperature of the water has been 
lower than that of the atmosphere, even when the atmosphere 
was saturated with vapour. 
It might at first view be supposed, that whether the cooling 
cause existed in the water or the land, the same consequences 
ought to result ; but the peculiar properties of water, to which 
1 referred in the beginning of the paper, render this impos- 
sible. W ater in abstracting heat from the atmosphere becomes 
lighter, and the warmer stratum rests on the surface, and its 
operation in cooling the atmosphere is extremely slow ; 
besides, the cooled atmospheric stratum remains in contact 
with it, and water cannot be deposited from vapour, when that 
vapour is rising into an atmosphere of a higher temperature 
than its own ; and the law holds good, however great the 
difference of temperature. Thus, August 26th, at sun-set, the 
day after a heavy fall of rain, and when the atmosphere was 
exceedingly moist, I ascertained the temperature of the Drave 
near Spital jn Carinthia, and though it was 14 0 F. below that 
of the air, yet the atmosphere above the river was perfectly 
transparent. 
It may be imagined, that without any reference to the 
cooling agencies of air from the land, mist may form upon 
rivers and lakes, merely from the loss of heat by radiation 
from the air, or the vapour itself immediately above the 
water; and that the phenomenon is merely one of the forma- 
tion of vapour, the source of heat being in the water ; and its 
deposition, the source of cold, being in the atmosphere; but 
it is extremehy improbable, that air or invisible vapour, at 
common temperatures, can lose any considerable quantity of 
heat by radiation ; and, if mist could be formed from such a 
