Notes on Hydrology. 89 



and must necessarily be warm, and to obtain that moisture 

 it must come over extensive areas of water — the ocean. On 

 coming in contact with cooler currents of air, cooler lands 

 and trees, the moisture is condensed in the form of rain, and 

 also when warm air, saturated with moisture, is mixed with 

 a cooler air also saturated a discharge of moisture takes 

 place, but to a very small extent. Where the vapours are 

 carried inland until they come in contact with high moun- 

 tain ranges, there the moisture is thrown upwards and is 

 condensed, and the air which is then cooled passes over the 

 mountain range with less moisture in it and in a state to 

 absorb moisture instead of discharging ; and it is found to be 

 almost universal that the coast-line of continents is wet, 

 and inland is dry, more particularly if the coast is bounded 

 by mountain ranges. 



It is found to be the case in India, where the south-west 

 monsoons, which blow towards the north in summer (the 

 sun being north of the equator), are laden with moisture from 

 the Indian Ocean come in contact with the Western Ghauts, 

 and the bulk of the moisture is discharged at about the 

 height at which the clouds float. At one station there — 

 Mahabulshwur — the rainfall for an average period of five 

 months per annum is 245 inches, upwards of 20 feet; in 1849 

 it amounted to 338 inches; 10 to 13 inches often fall in one 

 day, and as much as 130 inches in a month. The quantity 

 rapidly falls off at a higher elevation, and also lower down, 

 that is, above and below the average height of the line of 

 cloud flotation ; but on the eastern side of the mountain, only 

 11 miles distant, at another station — Paunchgunny — the 

 average is only 50 inches per annum ; and further east is the 

 Deccan (or dry country), where the rainfall is only from 16 

 to 20 inches. This is, 1 believe, the most remarkable instance 

 of the decrease of rain when intercepted by mountains. 

 Then, at the head of the Bay of Bengal, Calcutta, being low, 

 receives 60 to 80 inches per annum, but in some parts of the 

 Himalayas, north of Calcutta, the rainfall is said to amount to 

 as much as 600 inches per annum. The same rule holds 

 good in Great Britain. The moisture from the Atlantic is 

 condensed in Westmoreland and Cumberland at from 80 to 

 150 inches, whereas on the east side it varies from 18 to 24 

 inches per annum. 



The same rule holds good with regard to Europe, as we 

 recede from the Atlantic — Greenwich, 24 inches ; Paris, 23 

 inches ; Yienna, 19 inches ; St. Petersburg, 15 inches 



H 



