282 Mr G. A. Rowell on the Came of Storms. 



occupy a greater space to be buoyant at a distance from the 

 earth ; but as the elasticity of the air depends on its density, 

 the effect must be the same, that is, equal to a vacuum or 

 gradual abstraction at the level of the sea, of 860 inches of 

 air for every inch of rain that falls ; and above every square 

 mile over which such rain extends, a vacuum or rarefaction, 

 amounting to 1,997,952,000 cubic feet, whicli must be filled 

 up during the time the rain is falling by a rush of air from 

 other parts, causing a wind around the district, although 

 such wind may not always be felt where the rain is ac- 

 tually falling ; but simply shewing a depression in the baro- 

 meter, owing to the upheaving of the air into the vacuum. 



England is very free from excessive rains, yet it is by no 

 means uncommon to have a fall of \, \^ or f of an inch of 

 rain in a day, which, according to the above calculation, 

 must be sufiicient to cause moderate winds ; but the enor- 

 mous rains recorded by authors, are sufficient to account 

 for most tremendous storms. They are as follows : — 



These rains are all in temperate climates ; and there is 

 little doubt, that the extraordinary rains within the tropics 

 far exceed them, as the annual average fall of rain at the 

 Ghauts is 26 feet 2 inches, near 10 feet of which falls in the 

 month of July. 



Taking the first case (the fall of rain at Genoa), the aver- 

 age vacuum formed over every square mile during the 24 

 hours, must have been 2,497,440,000 cubic feet per hour, 

 41,624,000 per minute, or 693,733 per second; and in the 

 case of the fall of rain at Perth, 63,278,720 cubic feet per 

 minute, or 887,978 per second, for the whole time of the fall. 



The consideration of these excessive falls of rain, tends to 

 prove the theory, as they not only shew that tlie vacuum 



