AQUEOUS ATMOSPHERIC PHENOMENA. 



^M 



4G9 



A Thunder Storm. 



till the resistance opposed by the air becomes equal to their weight, when they continue 

 to fall with an uniform velocity. The velocity bears a certain ratio to the diameter of the 

 drops ; those of a thunder shower, which are large, pouring down faster than those of an 

 ordinary rain. The celerity of a small drop, T^th of an inch in diameter, he estimates at 

 1 1^- feet per second, upon acquiring its uniform velocity ; that of a larger one, ^th of an 

 inch, at 33^ feet. A great number of experiments have verified the remarkable circum 

 stance, that a greater quantity of rain falls upon a low site than upon one a little elevated 

 above it. Thus a rain-gauge placed at the bottom of a hill, will collect a larger amount 

 of water in a given time than another placed upon the summit. Dr. Heberden found that 

 the annual depth of rain at the top of Westminster Abbey was 12-099 inches ; at a lower 

 altitude, on the top of a neighbouring house, it was 18' 139 inches ; and on the ground, in 

 the garden of the house, it was 22-608 inches. M. Arago gives a similar result, from 

 observations made during ten years at Paris. On the terrace of the Observatory the 

 annual depth was 50-471 centimetres, or 19-88 inches; while thirty yards below, in the 

 court of the building, it was 56'37l centimetres, or 22'21 inches. Comparing, however, 

 an extensive tract of mountainous country with a low level district, the annual fall of rain 

 in the former greatly exceeds that in the latter, though contrary to the natural pre 

 sumption suggested by the fact, that the lower regions of the atmosphere are much more 

 saturated with vapour than the upper. At Keswick in Cumberland a mountainous 

 district the average annual depth of rain is 67*5 inches, while on the sea-coast it is not 

 half that amount. On the Great St. Bernard it is 63-13 inches, and at Paris only 21-26. 

 The description of Judea by the sacred writer, contrasting it with the flat lands of Egypt, 

 though not intended to be philosophic, is in harmony with the teaching of science respect 

 ing the important part performed by mountains in the general economy of the earth : 

 " For the land whither thou goest in to possess it, is not as the land of Egypt, from 

 whence ye came out ; but the land whither ye go to possess it, is a land of hills and val 

 leys, and drinketh water of the rain of heaven." By arresting the course of the clouds, 

 and producing a condensation of aqueous vapour when a warm current of air lights upon 

 their cold summits, the elevations contribute to precipitate the moisture of the atmo 

 sphere, often amid a terrible display of electric phenomena a blaze of fiery honours, 

 and the echo of heart-thrilling sounds. 



The statement respecting a greater amount of rain being collected by a low than an 

 elevated guage, in the same time, in a given district, is strikingly illustrated by Mr 

 Miller's report on the amount of precipitation in the lake regions of Cumberland and 

 Westmoreland. 



Seathwaite, near Derwentwater, . From June 1846 to November 1847, . 242 feet, . 193-09 inches. 

 Styhead, . 1290 u . 164-12 



Seatotler, ...... . 1334 . 155 75 



