38 



THE CLIMATE OF IRELAND. 



impart to the atmosphere in our latitudes, may be inferred from the 

 following note given by Marie Davy, from observations made by Captain 

 Duchesne in crossing the Atlantic from New York to France in 1865* : — 



The effect of the Gulf Stream upon the local temperatures in Ireland is 

 such that the isothermals crossing the island from east to west, decline from 

 the parallels of latitude, in accordance with the following observations, 

 viz. : — The mean temperature for the year at Dublin is about 1^.4 F. less 

 than at Westport ; for January it is 2°. J F. less; and for August i°4 F. 

 greater. 



of the 

 Ground. 



Amongst the conditions contributory to the general character of the 

 climate of the island, as well as to variation in local 

 Configuration temperature, is the configuration of the surface. If 



300 feet above the sea level be taken as the general 

 level of the lower parts of the country, about half its 

 area lies above this elevation ; and every additional 100 feet above 300 per- 

 ceptibly lessens the value of land, because of the effect of altitude upon 

 temperature. This was fully recognised by Sir R. Griffith.f In consequence 

 of the effect referred to, the mean temperature at 500 feet elevation near 

 Dublin, would be about equal to that at the sea-level at Londonderry or 

 Moville. The temperature falls approximately one degree F. for every 250 

 to 300 feet rise, in our latitude. The higher ground of the mountain groups, 

 moreover, tends to modify the direction and force of winds ; it produces 

 condensation of vapour reaching Ireland from the Ocean, which greatly 

 affects the temperature of the hilly regions, and adjacent low-l)'ing areas ; 

 and it partially drains the aerial currents of moisture, so that the precipita- 

 tion (rain) on the lee side of the hills, is not so great as it otherwise would be. 

 Every farmer knows the advantage of a southern aspect for his early 

 seed bed in spring. The sun at the Equinox is only 

 some 36° above the horizon at noon, in our latitude. 

 Aspect. ji^g heating power at this season, therefore, as w^ell as 



being lessened by sending its rays obliquely through 

 the moist atmosphere, is greatly diffused on level surfaces, and almost nil 

 on northern slopes. Concentration of the sun's heat and light therefore, 

 which is so desirable, can only be secured by arranging that beds bearing 

 seeds and plants, sliall be presented to it at as great an angle as convenient. 

 The following Table, prepared from data given in the Monthly Sum- 

 maries of the Meteorological Office, sets forth the number of hours of, and 

 percentage of possible, bright sunshine in the three growing months, March, 

 April, and May, at the only Irish stations which record it : for the sake of 

 comparison the records at two English stations are added. 



* " Meteorologie Generate, " p. 145. 



t " Guide to the Principles of Land Valuation," (Ponsonl)y, Dublin), p. 164. 



