262 Proximate Causes of certain Winds and Storms. 



the different portions of air only at the plane where they meet, and 

 this will be altogether inadequate to the production of a copious rain. 

 If their altitude be different, so that the one may glide past the other, 

 but in immediate contact with it, there will be a more considerable 

 mingling of the two, but still not such as is commensurate with the 

 effect observed. This hypothesis is besides encumbered with other 

 difficulties. Where shall we find the cause or causes that shall set 

 two currents in motion in' opposite directions, and make them flow on 

 amicably together, and in contact with each other for hundreds of 

 miles ? If they are of nearly equal coldness, no considerable effect 

 will follow from their mixture. If they differ greatly in their tempe- 

 rature, their specific gravity will be so widely different that they will 

 separate, the lighter flowing above, and the heavier below. If we 

 suppose that combination of circumstances which, according to these 

 views, would produce a condensation of the moisture of the atmos- 

 phere to happen occasionally ; it could not, like the fall of rain or 

 snow, be an every day occurrence. But if the air have commonly 

 in storms a vertiginous motion, the difficulty vanishes at once. The 

 warm strata at the surface will be carried upwards, and the cold 

 strata brought down from above, and as perfect a mixture of air of 

 very different temperatures produced, as any theory can demand. 



Franklin draws his illustration of the movement of the air during 

 our north-east storms, from that of the water in a canal, when the 

 gate by which it had previously been confined is raised ; and with 

 his views those of Dr. Hare appear nearly to coincide. Dr. Hare 

 appears to regard the warm moist air that rises from the surface of 

 the Gulf of Mexico, as the repository from which the rain and snow 

 are derived, the precipitation being caused partly by a diminution o( 

 capacity, undergone by it in consequence of its rarefaction as it as- 

 cends, and partly by its admixture with the under current of cold 

 air that comes in from the nordi-east, whilst it flows itself from the 

 south-west. The accuracy of these views may be questioned on a 

 number of different grounds. 



1. The precipitation arising from a change of capacity produced 

 by rarefaction, must be confined to the immediate neighborhood of 

 the gulf where the ascent and rarefaction take place. The rain and 

 snow descending upon the middle and northern states must therefore 

 be ascribed simply to the mixture of the lower surface or stratum of 

 the upper current of warm air flowing towards the north-east, and 

 die rppcr stratum of the current of cold air tomhz from that quarter. 



