Phenomena and Causes of Hail Storms. 251 



the clouds from opposite points of the compass. Thus a writer 

 in the American Journal of Science, describing a violent storm 

 that occurred in the state of New Jersey, adds, " I observed 

 then, and have many times observed since, that hail is usually 

 accompanied by contrary winds, which seem striving over our 

 heads for the mastery." And Beccaria I'ecognises the same fea- 

 ture of clouds congregated from opposite quarters. " While," 

 says he, "these clouds are agitated with the most rapid motions, 

 the rain generally falls in greatest plenty, and if the agitation 

 be exceedingly great, it generally hails *." 



We will now see how far the foregoing explanation corres- 

 ponds to the facts before enumerated. 



Why, then, are violent hail-storms attended by all the other ele- 

 ments of storms, — by clouds of intense blackness, and terrific 

 thunder and lightning ? Because the sudden concourse of a 

 wind exceedingly cold with one comparatively hot, ought, in 

 conformity with the known causes of these phenomena, to ex- 

 hibit them in their most energetic forms. All these atmospheric 

 phenomena are linked together, and the same causes, acting with 

 different degrees of enei-gy, produce each of them in its turn. 

 The mixing of portions of air differing but little in temperature 

 is sufficient to form clouds — if the temperature differs somewhat 

 more, the watery vapour may fall in rain — ^if the one portion is 

 hot and the other cold, more sudden and powerful rains are the 

 consequence, and thunder and lightning result from the rapid 

 condensation of watery vapour — and, finally, when a powerful 

 wind irom the regions of perpetual frost mixes with the heated 

 and humid air of a warmer sky, the same watery vapour descends 

 in hail. 



Why are such violent hail-storms confined to tlie temperate 

 climates, and why do they occur neither in the torrid nor in the 

 frigid zone ? This is a point of great difficulty, and the ques- 

 tion has never to my knowledge been satisfactorily answered ; 

 but I think we perceive something in the foregoing principles, 

 which may lead us to a correct understanding of it. We have 

 considered the case of two opposite winds from points differing 

 twenty degrees in latitude, one blowing north from the SOth, 



" Priestley, 341, Nidi. Jour. xxiv. 111. 



K 2 



