METEORIC RIVERS OR WATERFALLS. 427 



lowest at the mountains, and be above the mean at some 

 distance from the borders of the storm, in consequence of 

 the rapid outspreading of the air in the upper part of the 

 cloud in the region of the storm, and this effect will be felt, 

 especially in the north east of the storm, because the upper 

 region of the atmosphere in this part of the country moves 

 generally to the north east. Let h g represent the line, or 

 part of the annulus, where the barometer stands highest to 

 the north east of the storm, then will the wind blow both 

 ways from that line, and as it approaches the centre of the 

 storm at a, it will increase very much in violence because 

 the barometer is low there. 



When this wind reaches the mountain it will be obliged 

 to rise even before the centre of the storm has reached 

 there, and in rising will form cloud. Now this formation 

 of cloud will soon bring the centre of the storm to the east 

 side of the mountains, for the cloud which rises on the 

 west side will be pressed over towards the north east by 

 the upper current in the atmosphere. Thus will the centre 

 of the cloud be held constantly over the region just east of 

 the mountain. 1 



We are now prepared to answer a question which natu- 

 rally arises here. Why does the rain cease? By casting 

 the eye on the figure, it will be perceived that the air blows in 

 opposite directions from the annulus h g, and of course the 

 atmosphere sinks down there. Now as soon as the dry 

 atmosphere of the upper regions reaches the earth the sup- 

 ply of vapor is cut off from the storm, and the storm ceases. 

 This is one way in which the rain might cease, as it does 



1 If the mountain against which the wind blows is immoderately high, as 

 the Andes or the Himalaya, it is manifest that the rain will fall on the 

 windward side ; but it would be out of place here to assign the reason why 

 the wind blows for four or five months in the summer against the south west 

 side of the Himalaya mountains. 



