338 HISTORY OF 



curve or circular lines, so, having joined the 

 whirl, they ascend by a spiral motion, in the same 

 manner as the water descends spirally through 

 the hole in the tub before mentioned. 



" And as the lower air nearest the surface is 

 more rarefied by the heat of the sun, it is more 

 impressed by the current of the surrounding cold 

 and heavy air which is to assume its place ; and 

 consequently its motion towards the whirl is swift- 

 est, and so the force of the lower part of the whirl 

 strongest, and the centrifugal force of its particles 

 greatest. Hence the vacuum which encloses the 

 axis of the whirl should be greatest near the earth 

 or sea, and diminish gradually as it approaches 

 the region of the clouds, till it ends in a point. 



" If the vacuum passes over water, the water 

 may rise in a body or column therein to the 

 height of about 32 feet. This whirl of air may 

 be as invisible as the air itself, though reaching 

 in reality from the water to the region of cool 

 air, in which our low summer thunder clouds 

 commonly float ; but it will soon become visible 

 at its extremities. 



" As the whirl weakens, the tube may appa- 

 rently separate in the middle ; the column of 

 water subsiding, the superior condensed part 

 drawing up to the cloud. The tube or whirl 

 of air may nevertheless remain entire, the middle 

 only becoming invisible, as not containing any 

 visible matter." 



In connexion with the wonderful phenomena 

 above noticed, the following account of Meteoro- 

 lites will be perused with interest. 



