;}96 THE CLIMATE OF IRELAND, AND 



diminished at those places which are nearest to the track of their 

 centres. It has been found, accordingly, that there is an ine- 

 quality in the distribution of the atmospheric pressure in Ireland, 

 and that the minimum occurs in the north-western quarter of 

 the island. 



I now proceed, lastly, to the effects of the Grulf-Stream on the 

 humidity, and on the rain-fall, in this island. 



The amount of evaporation from the surface of water increases 

 rapidly with its temperature. Consequently the air above the 

 Gulf-Stream is loaded with vapour to a much greater degree than 

 that which rests on other portions of the Atlantic. This vapour 

 is borne to the British Islands by the south-west winds, which are 

 the predominating winds in this portion of the globe ; and, in 

 consequence, these islands have more than their average share of 

 humidity. The effect is, of course, greatest at those places which 

 the wind first reaches. It is, accordingly, greatest in Ireland, less 

 in England, and still less on the Continent of Europe, diminish- 

 ing with the distance of the place from the Atlantic. Thus, in 

 Paris (and probably in France generally) the mean amount of 

 vapour in the air is about 77 per cent, of the maximum which 

 it is capable of- holding. In London, it is 84 per cent. ; and in 

 Dublin it amounts to 88 per cent., which is about the average 

 for Ireland. 



The humidity is greatest, as we should expect a priori, on the 

 western coast of Ireland, and least on the eastern the former 

 being about 90 per cent., and the latter 85. The following Table 

 gives the mean humidity of the several months of the year at 

 Dublin. It is greatest in December, and least in June : 



