118 DE MILLER ON THE METEOROLOGY OF 



tering thermometers on Sea Fell and Gabel, buried under 12 to 18 inches of snow, 

 indicated a minimum of 8°, 9°, or 10°, the real 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 Sea Fell and the Gabel. f 



In 1852, the mean of the absolute monthly minimum temperature on Sea 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 



* I have only met with one instance of the presence of a strong hreeze 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-hook, — " Ascended Sea Fell, &c. There was a fresh hreeze and appear- 

 ance of rain on our leaving the valley at ll h 40 ra a.m., hut 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 evening. 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. 



■j- The writer saw a patch of snow on Sea Fell, on the 15th of June, 1843. 



