THE ENGLISH LAKE DISTRICT. 109 
at Seathwaite, and, in the Winter months of those years, 0:3 per cent. and 3:4 
per cent. respectively /ess rain fell on the mountains than in the valley. But, in 
1852, 3 per cent. dess rain fell in the Summer and 1:5 per cent. more in the Winter 
months, than descended in the subjacent valley; and, in 1853, the fall is less than 
in the valley, both in the Summer and the Winter months. In the years 1850 
and 1851, the relative excess of rain on the Stye, 948 feet above the Sea, was 27°6 
and 21°5 per cent., but in 1852 and 1853, only 8:1 and 9°7 per cent. respectively ; 
hence, in the memorably wet year 1852, this station received nearly 2 inches 
less rain than in 1851, and 21 inches less than in 1850. 
The above tables shew that on the mountains, the greatest depth of rain in- 
' variably obtains at Sparkling Tarn, 1900 feet above the sea level. The current 
which brings our principal supply of rain is the South-west. It is characterized by 
a high temperature—is generally at or near the point of saturation—and, in most 
heavy and continuous rains, the depth of the stratum of vapour is considerable, 
extending from a thousand feet or less above the sea to probably 4000 or 5000 feet 
above it. In passing over the comparatively level tract of country between the 
coast and the mountain ranges, rain is deposited, but with little diminution in 
the temperature of the gases or vapour. The current is at length arrested in its 
progress by the hills—the vapour in contact with the bases of the mountains is 
subjected to more rapid condensation, during which it gives out a portion of its 
latent heat in a sensible form, whereby the temperature of the surrounding mass 
of air and vapour is increased, and, by virtue of its increased elasticity, it rises to 
a greater height; the diminution of temperature due to the increased elevation 
causes fresh deposition—the surrounding medium is again warmed—the vapour 
ascends still higher—is farther cooled, and more water forced from it; and thus, 
the same operation is continued and repeated, so long as an adequate supply of 
vapour is furnished from beneath. Hence, in the upper regions of the atmosphere, 
there is a vertical as well as a lateral current of vapour constantly rushing in to 
supply the loss by precipitation. 
In ascending from the valley, the amount of vapour which the atmosphere is 
capable of supporting or containing in mechanical combination is found to diminish, 
while the difference between the air and dew point temperatures also gradually 
decreases. There must therefore be a point of elevation, where the quantity of 
vapour and the degree of humidity will combine to produce a maximum deposit 
of rain in a given time; and this plane of greatest condensation is found, in the 
English Lake District, at or about 2000 feet above the sea-level. 
It does not follow, from what has just been stated, that the same law would 
hold good in the open atmosphere, (supposing it were possible to plant a gauge 
therein at an altitude of 2000 feet) because the rate of cooling upwards is much 
more sudden in ascending on the surface, than obtains in rising abruptly fom the 
‘surface, as in a balloon; consequently, the temperature at any given elevation on 
VOL. XXI. PART I. 2G 
