246 Prof. Hennessy on the Distribution 



not merely upon our western seaboards, but all around the entire 

 coast-line of the British islands. They are thus situated pre- 

 cisely under such conditions as naturally lead us to expect to 

 find the distribution of heat over their surfaces such as would 

 be indicated by groups of isothermal lines conforming to the law 

 here adduced. 



There are, in addition, some physical peculiarities in the struc- 

 ture of Ireland, which probably enhance the influence of the 

 ocean upon the relative thermal conditions of its maritime and 

 its inland portions. It is nearly surrounded at its coasts by 

 ranges of mountains or lofty hills ; and its interior consists chiefly 

 of flat and low-lying plains. Eight such littoral ranges of 

 elevated ground can be distinctly traced on a map of Ireland, 

 each separated from its neighbour by some great outlet for the 

 drainage waters of the interior. These elevated masses may be 

 traced, 1, on the north-west coast in Donegal j 2, on the west 

 in Mayo and Galway ; 3, along the south-west coast in Kerry 

 and Cork ; 4, towards the South in Waterford ; 5, on the east 

 coast in Wicklow and ^A'^exford ; 6, on the north-east coast in 

 Down ; 7, towards the north-north-east in Antrim ; and 8, near 

 the north coast in Londonderry. The first of these groups trends 

 principally from N.E. toS.W. The second from N. to S., with 

 some nearly perpendicular offshoots. The fourth from E. toW. ; 

 the fifth from S.S.W. to N.N.E. ; the sixth from S.W. to N.E. ; 

 the seventh is a rather irregular group of hills ; the eighth trends 

 from E. to W. It thus appears that the general direction of each 

 of these groups is nearly parallel to the general direction of the 

 adjoining coast. The only extensive line of coast which is not 

 backed by a hilly or mountain barrier is that lying between the 

 Wicklow and Mourne mountains. 



Although it would be difficult to estimate the precise influence 

 of these elevated masses in obstructing interchanges between 

 the air surrounding the coast and that of the interior, they 

 doubtlessly must produce some effect. It is at least obvious 

 that moist and warm currents, encountering such masses, would 

 lose with a portion of their moisture some of their heat, and 

 would, on reaching the inland plains, be observed by the 

 inhabitants colder as well as drier than the same winds had 

 been noticed hy those residing on the coast. 



The considerable opening from the interior towards the sea, 

 which has been just referred to, happens to be situated in the 

 direction of those winds which blow least frequently in Ireland, 

 and which at the same time possess the least moisture and 

 warmth. 



Although observations on temperature have hitherto been 

 made at very few stations in Ireland, it is still possible to com- 



