468 PHILOSOPHY OF STORMS. 



and others of a similar kind, I am very doubtful if an up- 

 ward vortex of air, either upon a limited or an extended 

 scale, (except upon the principle of intermixture, 1 and also 



same direction with the upper, and with the same velocity, which can only 

 be the case in this latitude, when the wind is from some southern or south 

 western direction, tfren the columns can rise to a great height without being 

 broken, and this is one reason why a southerly wind is favorable for rain. 

 These observations apply exclusively to the generation of a rain cloud, and 

 not to the phenomena which occur after a great rain cloud is generated. Af- 

 ter that is done, the cloud has a self-sustaining power, and frequently con- 

 tinues as violent in the night as in the day, and if even it should be found to 

 discharge more rain in the night than in the day, as asserted above, it would 

 not be inconsistent with my theory. 



1 The doctrine of the intermixture of airs at different temperatures pro- 

 ducing rains, will not bear the test of examination. 1 demonstrated, in the 

 very essays here criticised, as the reader will see in the Journal of the Frank- 

 lin Institute for 1836, that if the two halves of the atmosphere, the upper and 

 lower, one at the temperature of 80 and the other zero, both saturated with 

 vapor, should be mingled together by magic, (for they cannot be mingled by 

 any causes in nature,) that the caloric of elasticity given out in one of our 

 great thunder storms, (5.1 inches of rain) if communicated to the mass of air 

 so mingled, would leave the whole about 20 hotter than the hottest half be- 

 fore the mixture. But why suppose a mixture in case of an upward motion 

 of air, as it is here supposed, if it goes up to where the barometer would stand 

 fifteen inches, it would cool without mixture at least 85, as I have demon- 

 strated by experiment, if no allowance is made for the caloric of elasticity 

 given out by the condensing vapor. 



And if any one will carefully watch a cumulus cloud while forming into 

 a nimbus, if he is properly situated for seeing the whole phenomena, he will 

 observe a wonderful stillness in the borders of the cloud, while it is puffing 

 out at the top, as if it were tl blown into below by a pair of great bellows." (70.) 



He will see the lower part of the cloud much agitated, and flocculi darting 

 in from the borders towards the centre, and finally, small clumps of clouds 

 suddenly forming some distance below the black base, and darting up into 

 that base, " like sky rockets;" in short, the whole phenomena corresponding 

 precisely with the supposition of an upward motion of the air, both below and 

 above the base of the cloud. If this cloud is formed from the mixture of aiis 

 of different temperature, which I have shown could not be, on other grounds, 

 I think it is certain that it could not assume the present form. If it were 

 formed of strata of air, one over the other, and moving in different directions, 

 so as to mingle between them and produce cloud, then the cloud would have 

 a flat appearance, and could not possibly rise into a pyramid of six or eight 

 miles in height, in a very short space of time, in regular form. 



