FALLS OF RAIN IN CUMBERLAND. 



201 



carried forward horizontally by the wind, and will reach the 

 earth at a part beyond that over which it was formed. 



Now, to apply this general statement and reasoning to 

 the case under consideration, let us suppose that air satu- 

 rated with vapour of the temperature of 59" passes from the 

 sea-coast, near Ravenglass, towards the mountains as a 

 south-west wind. When this wind reaches land 300 feet 

 high, it will be cooled by ascent P, and will have all the 

 vapour condensed that is contained between a dew-point 

 of 59** and one of 58°. When it reached land 600 feet high, 

 2° of vapour would be condensed ; 900 feet 3°, and so on 

 in succession, 1° more for every 300 feet of height up which 

 the air was forced mechanically. Add to this the vertical 

 ascent produced by heat from condensation, and the actual 

 progressive motion of the condensing vapour will be inter- 

 mediate between the two. Supposing the two forces to be 

 equal, the mass would proceed forward, ascending at the 

 angle of 45". Sty-head Pass is 1,290 feet high — the atmo- 

 spheric mass, therefore, when it reached Sty-head would 

 be cooled, say 4°, and it would be liable to be carried over 

 the head of the Pass, rising at an angle of 45°. We might 

 therefore expect, from the known laws of condensation of 

 vapour, and of the action of wind, that, under the circum- 

 stances described, a larger amount of rain would fall beyond 

 Sty-head, than either in the approach to it, or on the top 

 of it ; and accordingly it is the fact that a larger quantity 

 of rain falls in Seathwaite, which is a little beyond the Pass, 

 than in any part between Seathwaite and the sea. 



In such a locality the saturated air, forced by the rise of 

 the land to ascend, entering the wide mouth of the Valley, 

 which contracts in breadth as it proceeds, rushes through 

 the narrow gorge in the upper part, and over the top of the 

 mountain pass, with great velocity and force ; condensation 

 therefore will take place to a greater extent along this par- 

 ticular and comparatively low line, than where the ridge 



2 D 



