16 
On the Production of Mist. By Joun Davy, M.D., F.R.S. 
Lond. and Ed., &c. 
One cause has commonly been assigned for the production 
of mist, viz., the access of cold air and its admixture with 
warmer air saturated, or nearly saturated, with moisture, such 
as that resting on the surface of great bodies of water—the 
sea, for instance, lakes, and large rivers—and so strikingly 
exemplified in our autumnal and early winter fogs, when the 
bodies of water alluded to, owing to the heat absorbed during 
the warm summer season, are of much higher temperature 
than the inflowing air, especially if the wind be from a nor- 
therly quarter. 
Another cause, and one which has had less attention paid 
to it, is of an opposite kind, and acting mostly at a different 
season—viz., a2 mild moist air coming in contact with a colder 
air, equally humid, incumbent on cold surfaces, whether of 
water or land, towards the end of winter and the beginning 
of spring. The production of mist in this way, at the times 
mentioned, may often be seen, especially during a thaw 
with a change of wind from the north and north-east to the 
south and south-west. In the Lake District. I have fre- 
quently observed it, when passing along Windermere under 
the circumstances described, and when, on trying the tem- 
perature of the water of the lake and the air over it, that of 
the former has been found to be ten or more degrees lower than 
that of the latter. In the same district, under the like condi- 
tions, the formation of mist on the hills is often to be witnessed 
—their surface-temperature at the time being many degrees 
below that of the mild moist air impinging on them. 
One of the peculiarities of this later mist—if it may be so 
distinguished from the earlier—is, that it is low, rising but 
little above the surface, and never occurring at least over water, 
except with the gentlest breeze. Associated with this pheno- 
menon is another, and one more noticeable—the precipitation 
of moisture on walls and flagged floors so situated as not to 
have had the benefit of fire, and consequently liable to ac- 
quire, during any severity of cold in winter, a low temperature, ° 
