Mr G. A. Rowell on the Cause of Storms. 283 



formed is sufficient to account for violent storms, but they 

 also shew that there must be a strong current of air and 

 vapour to these places, as it would otherwise be difficult to 

 conceive how such a quantity of water could be accumulated 

 over any part of the earth ; in the case at Genoa, the fall 

 continued for 24 hours, and the tremendous rain of near 10 

 feet, which usually falls in the month of July at the Ghauts, 

 can only be accounted for by a continuous flow of air and 

 vapour to those parts. 



The reasoning already advanced will account for the fall 

 in the barometer during rain ; its falling previous to rain I 

 would explain as follows: — As the density of air decreases 

 as we recede from the earth, the particles of vapour, with 

 their coatings of electricity, must occupy different spaces to 

 float at difi^erent heights, as water is 860 times heavier than 

 air at the level of the sea, 1083 times at one mile high, 

 1363 times at two miles, 1716 times at three miles, 2160 

 times at four miles, and 2719 times at five miles high, there- 

 fore, vapour floating at any height, must part with a portion 

 of its electricity before it can sink to a lower elevation ; thus, 

 if the air become in a fit state to conduct the electricity from 

 the clouds or invisible vapour over any place, as the passage 

 of electricity is so rapid, its escape must occasion a partial 

 vacuum, which would cause a corresponding sinking in the 

 barometer. In assigning these causes for the fluctuations 

 in the barometer, I allude only to the changes previous to 

 and during rain, as other fluctuations are caused by high 

 winds, change of temperature, <fec. 



The increase of wind which sometimes precedes a storm 

 of rain in windy weather, hardly requires an explanation. As 

 the rain falling, and electricity escaping from the cloud, act 

 with a degree of pressure on the air under the cloud, this 

 pressure must increase the force of the wind preceding the 

 cloud, and at the same time check the wind that follows it, 

 causing a sort of lull or calm. 



It is probable that water-spouts are, owing to the rapid. 

 escape of electricity and fall of heavy rain from a dense 

 cloud, causing a vacuum into which the neighbouring parts 

 of the cloud are forced, the electricity from which being in- 



