243 Meteorological Journal. (Marcu, 
ree the very circumstance of its production abates the first rigour 
of the cold. Just before this snow the air was extremely moist; the 
snow cleared it of an inch and a half, nearly, of water, and it has 
since indicated considerable dryness. Now it is quite probable that 
the vapour which afforded this water was found, by the supervening 
N. E. current, diffused in our local atmosphere, and by it decomposed. 
In this case the whole of the latent or constituent heat given out by 
the vapour in passing to the solid state, must have gone to raise the 
temperature of that current. Hence a considerable interval, of gradually 
increasing cold, before we experienced its extreme effects; during 
which, too, the earth got provided with its accustomed covering. 
After a copious fall of snow an observer may find, in the scenery 
which it forms, some things on which to exercise his powers of re- 
flection. The pensile drifts, which in a mountainous country are 
objects of just alarm, may be contemplated, here, to discover the 
principles of their construction, and the manner in which they rest on 
go narrow a base. When the sun shines clear, and the temperature is 
at the same time too low for it to produce any moisture, the level 
surface may be found sprinkled with small polished plates of ice, which 
refract the light in colours as varied and as brilliant as those of the 
drops of dew. At such times, there are also to be found on the 
borders of frozen pools, and on small bodies which happen to be fixed 
in the ice and project from the surface, groups of feathery crystals, of 
considerable size, and of an extremely curious and delicate structure. 
From the moment almost that snow alights on the ground, it begins to 
undergo certain changes, which commonly end in a more solid crys- 
tallization than that which it had originally. A notable proportion 
evaporates again, and this at temperatures far below the freezing point. 
On the night of the 10th instant I exposed 1000 grains of light snow, 
spread on a dish, (which had previously the temperature of the air) 
of about six inches diameter. In the first hour after dark it lost five 
grains; in the second, four grains; in the third it acquired a grain, 
the wind having changed, and the temperature, which had been falling 
from 25°, inclining to rise again, The hygrometer was at 50°, with a 
gentle breeze at east. In the course of the night the total loss was 
about 60 grains. This evaporation from snow may very well supply 
the water for forming those thin mists, which appear in intense frost : 
and the slight increase during a part of the time, in this experiment, 
may throw light on the formation of the secondary icy crystallizations 
above-mentioned. It appears that the air ina still frosty night becomes 
partially loaded, either with spiculse of ice, or with particles of water, 
at a temperature below freezing, and ready to become. solid the 
moment they find a support. Hence the rime on trees, which is found 
to accumulate chiefly on the windward side of the twigs and branches. 
As to those more copious mists, of the modification stratus, which 
accompany the setting in of long frosts, I conceive them to originate 
in part from the yet unfrozen rivers, and other waters, near which 
they are most abundant; in part from the moisture of the earth itself : 
for it is contrary to experience to suppose, that the frozen state of the 
surface can prevent the ascent of vapour from the porous soil below : 
which will continue to emit it, until its temperature becomes, by the 
gradual penetration of the frost, nearly on a level with that of the 
cold air then constantly flowing over it, though too gently to disperse 
the cloud formed. 
Tottenham, Second Month, 20, 1816. L. HowarpD. 
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