EXAMINATION OF REID'S STORMS. 215 



must have come downwards in the centre with very great 

 velocity, a velocity calculated in article 88, unless the 

 whirling motion extended to so great a height that the air 

 at the surface of the atmosphere could not get in. 



If indeed the rotary velocity was much greater in the 

 middle region of the air than at the surface of the earth, or 

 the upper regions, then the air would rush upwards below, 

 and downwards above, towards the middle region, and the 

 cloud there formed, if one should be formed, would be seen 

 whirling round with great velocity and spreading outwards 

 with proportionate rapidity. In this way, large quantities 

 of the upper part and lower part would be mingled together 

 and it seems to be generally, though erroneously, believed, 

 that the upper part, being much colder than the lower, when 

 they meet and mingle, condensation of vapor would be the 

 result. But as it is known from experiment, that if the air, 

 at the temperature of 32 at the surface of the earth, should 

 rise in the atmosphere to where the air would be expanded 

 into double the volume, it would be colder by about 90, 

 and if the air should sink from the surface of the atmos- 

 phere to where the barometer stands 15 inches, it would rise 

 in temperature more than 90, it follows that when these two 

 masses of air met, the upper mass would be the warmest, 

 and its capacity for vapor being thus very much increased, 

 its tendency, on mingling with the lower air. would be to 

 prevent the formation of cloud, and if a cloud was formed 

 at all, it would be by the cold of the lower portion. 



But besides the impossibility of finding any cause for this 

 whirlwind in mid-air, it is contradicted by the whole ap- 

 pearance of the cloud connected with a tempest, whenever 

 an observer is so situated as to see the whole cloud. For 

 the circumference of the cloud always appears almost mo- 

 tionless, while the tempest is raging below with the greatest 

 fury. And the upper part of the cloud, instead of rolling 



