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IX. Sow? observations on the formation of Mists in particular 
situations. By Sir H. Davy, Bart. F. R. S. V. P. R. T. 
Read February 25, 1819. 
All persons who have been accustomed to the observation 
of Nature, must have frequently witnessed the formation of 
mists over the beds of rivers and lakes in calm and clear 
weather after sun set ; and whoever has considered these 
uhenomena in relation to the radiation and communication of 
A 
heat and nature of vapour, since the publication of the re- 
searches of M. M. Rumford, Leslie, Dalton, and Wells, 
can hardly have failed to discover the true cause of them. 
As, however, I am not aware that any work has yet been 
published in which this cause is fully discussed, and as it 
involves rather complicated principles, I shall make no apology 
for offering a few remarks on the subject to the Royal 
Society. 
As soon as the sun has disappeared from any part of the 
globe, the surface begins to lose heat by radiation, and in 
greater proportions as the sky is clearer; but the land and 
water are cooled by this operation in a very different manner: 
the impression of cooling on the land is limited to the surface, 
and very slowly transmitted to the interior ; whereas in 
water above 45 0 Fahrenheit, as soon as the upper stratum 
is cooled, whether bj' radiation or evaporation, it sinks in the 
mass of fluid, and its place is supplied by warmer water from 
below,, and till the temperature of the whole mass is reduced 
