118 DR MILLER ON THE METEOROLOGY OF 
tering thermometers on Sca Fell and Gabel, buried under 12 to 18 inches of snow, 
indicated a minimum of 8’, 9°, or 10°, the veal temperature of the air at these 
elevations must have been considerably below the zero point of FAHRENHEIT’s scale. 
The comparatively high readings of the night thermometers in the winter 
months being thus fully accounted for, I have endeavoured to discover whether there 
are any circumstances or conditions ordinarily present during the night hours, 
which may tend to modify the temperature of the upper regions of the atmosphere 
when the sun is below the horizon. The cooling effect produced by terrestrial radia- 
tion on the stratum of air in immediate contact with the earth, appears to extend to 
the ordinary height of a thermometer suspended in the air (4 feet), since we find 
the coldest nights, both on the surface and at 4 feet above it, are always those in 
which the principal conditions essential to free radiation are present—a serene 
and unclouded sky. The atmosphere is usually in more rapid motion on high 
lying lands and hills, than on the plains. Hence, plants growing on high exposed 
ground, where the air is more disturbed than in the valleys, suffer less from frost. 
Now, to whatever extent the temperature at 4 feet above the earth’s surface is 
depressed by radiation, the depression at an equal altitude above the tops of the 
mountains will in general be much less, inasmuch as a calm state of the air very 
seldom obtains in these elevated regions.* The lateral atmospheric currents, 
rarely absent, will supply a large portion of the heat lost by conduction consequent 
on the radiation from the very limited areas constituting the mountain tops or 
peaks. Moreover, the large amount of heat thrown off by the earth’s crust be- 
tween sunset and sunrise may tend to keep up the temperature of the upper 
strata of the air during the night. But for this supply of heat communicated by 
terrestrial radiation, ice and snow would probably form much earlier in the autumn 
and perhaps rarely be absent during the summer months, on such elevated peaks 
as Sca Fell and the Gabel.+ : 
In 1852, the mean of the absolute monthly minimum temperature on Sca Fell 
at 4 feet above the top, and perfectly protected from radiation, was 2°6 less than 
the temperature on the grass at Seathwaite similarily determined. 
The mildness and equability of the climate in our sequestered mountain valleys 
was further exemplified during the periods of extreme cold which prevailed over 
the country generally, in December and January last. The lowest temperature 
* T have only met with one instance of the presence of a strong breeze in the valley, when the air 
was quite motionless on the top of a mountain. On the 21st of April 1848, I find the following 
memorandum in the register-book,— Ascended Sea Fell, &c, There was a fresh breeze and appear- 
ance of rain on our leaving the valley at 11 40™ a.m, but before attaining the summit of Lingmell 
(1778 feet) the air became perfectly calm, and so continued till we had again reached the foot of the 
mountain. We were surprised to find that a strong breeze had prevailed in the valley during our 
absence on the Fell; and it continued to blow fresh throughout the eyening. The clouds (Cumuli) 
were evidently electric, and generally below the summit of Sea Fell. We passed through one in de- 
scending, and a distant peal of thunder was heard from the top. 
+ The writer saw a patch of snow on Sca Fell, on the 15th of June, 1843. 
_—* 
pe na) msc tening 
