THUNDER-SHOWERS. 341 



the summits of the mountain-ridge, from the valley of the Connecticut, 

 and also from the sea. This moist air, meeting with the general cur- 

 rent from the southwest, piles up an immense mass of cumulus cloud, 

 of many square miles in extent. So long as the intense heat prevails, 

 this cloud increases in size ; grows black and blacker with its dense 

 vapor, and casts a gloomy, lurid glare over the face of Nature, darker 

 than that of any eclipse. The vapor, pushed up by the ascending 

 currents of heated air, attains to a great height above the sea, where 

 the temperature is very low. But finally, at that hour of the after- 

 noon when the heat begins to decline, the accumulated vapors, no 

 longer augmented or sustained by heated air from the valleys below, 

 fall in rain. 



The eftect of large cold drops of water, or perhaps of ice, making 

 altogether millions of tons in weight, falling from a great height into 

 a deep, narrow valley, is, not only to beat down the air into that valley, 

 but to chill the air there ; and the cold air, seeking the lowest level, 

 tends to rush down the valley, at first near the sui'face of the earth, 

 but growing deeper and deeper, until the cloud itself is borne away 

 on the swift-rushing air-freshet of its owai making. 



The land beginning to cool with the declining sun and the cooling 

 rain, causes the southerly breeze to slacken and die away, and the 

 stoi'm-cloud rushes on unobstructedly down the West River and the 

 Connecticut, deluging and fertilizing the fields along its course, while 

 its quick lightning and oft-repeated claps of thunder flash and resound 

 among the reverberating hills. 



The cloud passes on, and often the sinking sun comes out from be- 

 hind it ; the late hushed and frightened birds gush forth with new 

 song ; myriad drops hang glittering on the spray ; the green is flushed 

 with a brighter, fresher hue, and the glowing rainbow smiles serenely 

 from the dark, retiring, and still grumbling storm. 



This storm is followed the next day by delightfully clear weather, 

 with a cool, exhilarating breeze from the northwest ; though this is 

 not always the case, the cloud sometimes overspreading the sky, losing 

 its motion, and leaving the air damp and murky. 



The thunder-shower, as w^e have thus described it, though limited 

 to a small disti'ict of country, may be regarded as the type of all similar 

 showers that occur in mountainous regions everywhere. Numerous 

 modifications, however, of local origin will occur, due to various 

 causes ; and it would be a highly-interesting and valuable study to as- 

 certain these causes for every particular case. 



Yet as to whether the moving force of the thunder-gust is limited 

 wholly to the causes here given, may well admit of a question. It is 

 not improbable that a cloud, from its great height, may penetrate a 

 high upper current from the northwest, and that both this upper and 

 the lower current may contribute to its rapid motion of translation. 

 It is well that these thunder-showers are movable, instead of being 



