ON AQUEOUS AND IGNEOUS METEORS. 557 



afford, by means of springs and rivers, a constant supply for the use of 

 man and of other animals in distant parts. The upper regions of the 

 atmosphere are however by no means the principal sources of rain in ordi- 

 nary climates, since a gage placed on a very high building seldom collects 

 more than two thirds as much rain as another standing on the ground 

 below :* and the effects of mountains in collecting rain are perhaps 

 chiefly derived from the ascending currents which they occasion, and by 

 which the air saturated with moisture is carried to a higher and a colder 

 region. 



The Abyssinian rains are the causes of the inundation of the Nile : they 

 last from April to September ; but for the first three months the rain is 

 only in the night. The inundation, in Egypt, begins at present about 

 the 17th of June ; it increases for 40 days, and subsides in the same time ; 

 but the ancient accounts, as well as some modern ones, assign a longer 

 duration to it. The river Laplata rises and falls at the same times as the 

 Nile. The Ganges, the Indus, the Euphrates, the river of Ava or Pegu, 

 and many other large rivers, have also considerable inundations at regular 

 periods. In many other countries there are seasons at which the rains 

 seldom fail to recur ; and sometimes the periodical rains are different in 

 different parts of the same country. Thus the coast of Malabar, which is 

 to the west of the Gate mountains, or Gauts, enjoys summer weather, 

 without rain, from September to April, while that of Coromandel, which 

 is on the eastern side, experiences all the rigours of its winter ; being at 

 this time exposed to the influence of the north east trade wind. Vicissi- 

 tudes of a similar nature are also observed on the north and south sides of 

 the island of Jamaica. The mean fall of rain in London is about 23 

 inches ; at Exeter, which is nearer to the Atlantic, 33 ; the average of 

 England and Wales is 31. 



The evaporations and precipitations, and probably also the condensations 

 and expansions, which take place on a large scale in the atmosphere, and 

 in the clouds, cannot fail of producing changes in their electrical qualities, 

 and these changes appear to be the principal sources of the phenomena of 

 thunder and lightning. The clouds, when electrified, being more or less 

 insulated by the interposition of the air, exhibit attractive and repulsive 

 effects, and are discharged by explosions, either among themselves, or 

 communicating with the earth, in the same manner as bodies which have 

 been electrified by artificial means ; they also sometimes produce, in the 

 neighbouring parts of the earth, and in the animals on its surface, a state 

 of induced electricity ; and in this case the returning stroke, or the sudden 

 restoration of the equilibrium, when the electricity of the nearest clouds is 

 imparted to the more remote, may be fatal, without any appearance of an 

 immediate discharge, at the place where the animal stands. 



We can, however, by no means precisely ascertain in what manner all 

 the electrical phenomena of the atmosphere are produced. It appears from 



* From the observations of Prof. Phillips at York, the fall of rain during twelve 

 months ^ as 25'7 in. on the ground, 19'8 in. 44 feet above the ground, and not quite 

 15 in. 213 feet above it. Rep. of Br. Ass. 1834, p. 560. 



