CLIMATE 51 



The height and configuration of the land have a powerful 

 influence on the rainfall. Where high hills intercept 

 moisture-laden winds from the sea, the fall is much greater 

 than it is in low-lying districts. Warm air holds more 

 vapour in suspension than cold air ; and as the moisture- 

 laden winds that blow in from the sea rise over the hills 

 they quickly cool and precipitate part of their moisture in 

 the form of rain or fog. At the low-lying lands of the 

 Rhinns of Islay the average fall is probably under 40 inches ; 

 in the more hilly district round M'Arthur's Head in 

 the same island it rises to about 60 inches (37 years' 

 average, 1862-98). In Tiree, where much of the land 

 is scarcely higher than sea-level, the annual fall is little 

 more than 40 inches; at Lochbuie, which lies under 

 the high mountains of Mull, it is 90 inches. At 

 Stornoway the annual fall is about 48 inches (1856- 

 98), at Portree 88 inches, and at Dunollie and Oban about 

 60 inches. 



A comparison of the returns from the East Coast with 

 those from the West shows that the rainfall on the West 

 Coast is much greater than it is on the East, on no part of 

 which does it reach 40 inches, while it is less than 30 on 

 the north-east coast of Caithness, the low-lying lands to the 

 south-east of the Moray Firth, along the East Coast to Burnt- 

 island, and on the low grounds of Mid and East Lothian. 

 Over a large part of the south-east of England, from the 

 Humber to the estuary of the Thames, the average rainfall 

 varies from about 22 to 25 inches. The average number of 

 days on which rain falls annually on the West Coast is about 

 200, and on the East Coast 150. Great variations, however, 

 occur in the annual rainfall, and a short series of observa- 

 tions, if taken as indicating the average rainfall of a particular 

 district, might prove very misleading. Even a decade is not 

 a long enough period to get a true mean. The seventies 

 were a wet decade, which, if taken alone, would lead us to 



