376 Professor Olmsted's Reply to Dr. Christie. 



there is usually, if not always, a change of direction in the wind ; 

 that is, the wind blows from a different quarter after the storm, and is 

 often exceedingly cold when the quantity of hail that falls is too small 

 to produce so great a change. 



Dr. Christie is under a mistake in supposing that my explanation 

 of the causes of hailstorms, requires that these storms should never 

 occur in the torrid zone, except in the region of high mountains. 

 So far from this, the theory demands that hailstorms should occur 

 wherever such hot and cold blasts of air, as he mentions, meet and 

 mix together. For obvious reasons assigned in my paper, they do 

 not often meet in the torrid zone, and accordingly hailstorms are 

 much less frequent there than in the temperate zones. The two 

 very respectable authorities which I quoted,* inform us, the one that 

 they never occur in the torrid zone, and the other that they are never 

 met with, except at an elevation of one thousand five hundred or two 

 thousand feet. It appears, however, from the facts adduced in the 

 foregoing article, that there are other situations within the torrid zone 

 where hailstorms occur ; but still, so far as we can gather the cir- 

 cumstances from the brief statements of Dr. Christie, these storms 

 result from the same causes as were assigned for hailstorms in gener- 

 al, namely, from the sudden meeting of blasts of very hot and very 

 cold air. 



I beg leave to add one remark m*re. Although I have endeav- 

 ored to show the precise manner in ^vhich these hot and cold blasts 

 meet, and hence, as I suppose, furnisbed a probable explanation of 

 the extraordinary fact, of the much greater frequency of hailstorms 

 in the temperate, than in the torrid or the frigid zone, yet should 

 these blasts meet in any other manner, — should cold and hot portions 

 of air meet either by the subsiding of cold strata from above, as 

 maintained by Professor Mitchell, f or should the opposite kinds of 

 winds be mixed together in the form of. whirlwinds, as maintained by 

 Mr. Redfield, J the leading doctrine which I have advanced would still 

 be true, that hailstorms result from tliC mixture of blasts of hot and 

 cold air, and not from any agencies of electricity, to which they have 

 been more commonly ascribed. 



Respectfully and truly yours, 



Deni^on Olmsted. 

 Yale College, June 17, 1831. 



* Recs' Cyclopedia, and the Edinburgh EncyclopEedia. 

 f Amer. Jour. Vol. XIX. 1 Ibid. 



