THE CURRENTS OF THE ATLANTIC. 397 



The distribution of rain is very unequal. In the east of Eng- 

 land, the annual rain-fall is between 20 and 25 inches only ; in 

 the west of Ireland, it is between 40 and 50 inches. In Ireland, 

 in the year 1851, the greatest amount of rain fell at Cahirciveen, 

 and the least at Portarlington, the amounts being 59*4 inches, 

 and 21*2 inches, respectively. The mean rain-fall for the whole 

 island, in that year, was 34'5 inches. 



The causes already adverted to explain, in part, the distribu- 

 tion of rain. The vapour which is borne to us by the south- 

 westerly winds is partly condensed into rain when the air is 

 cooled by contact with the land. The chief condensers are the 

 mountains, because they interpose the greatest obstacle to the 

 movement of the vapour-laden air. Accordingly the high moun- 

 tains of Kerry, which offer the first barrier to the progress of these 

 winds, bring down on their flanks the largest amount of rain ; 

 and, generally, the rain-fall is greatest on the western and south- 

 western coasts, while the places of least rain are either inland or on 

 the eastern coast. The disparity is greatest in winter, when the 

 clouds are low ; in summer, when they are high, they escape the 

 condensing effect of the land over which they pass, and the rain is 

 more evenly distributed. 



The amount of rain is always considerable in the neighbour- 

 hood of a mountain chain or group, except at places to the east- 

 ward of it, where it is small. Thus, the places of least rain in 

 Ireland Portarlington, Killough, and Dublin all lie to the 

 north-east of a mountain range ; while the places of greatest rain. 

 Cahirciveen, Westport, and Castletownsend are all in the 

 vicinity of high mountains, but on a different side. All this is 

 readily understood from what has been stated. The prevailing 

 wind is the south-west, which comes to us laden with the vapour 

 of the Gulf-Stream, and this vapour is precipitated chiefly on the 

 flanks of the mountains. And the same cause protects the region 

 over which the same wind next passes the east and north-east 

 the air having been deprived of its excess of vapour before arriv- 

 ing there. 



The distribution of rain throughout the year in Ireland will be 

 understood from the following numbers, which give the mean rain- 

 fall in each month at Dublin, as deduced from the observations of 

 the eleven years (1841-1851). The mean yearly rain-fall is 29'1 

 inches. 



