oj Heat over Islands. 



247 



pare what has been done with the principles here put forward. 

 During the year 1851, a series of meteorological observations 

 were conducted under the management of a committee of the 

 Royal Irish Academy ; and the stations, although not numerous, 

 were fortunately so distributed as to enable us to combine their 

 results in such a way as to clearly illustrate the thermal con- 

 ditions of the island. The most important results are contained 

 in the Rev. Dr. Lloyd's valuable memoir on the Meteorology of 

 Ireland *. 



As to temperature, the observations had a twofold appli- 

 cation : 1st, those referring to the temperature of the sea, and, 

 2ndly, those relating to the temperature of the air. A com- 

 parison of both classes of observations establishes the fact of an 

 excess of temperature of the sea over the air, in 1851, amounting 

 to 3'*8 Fahrenheit. The mean temperature at Portrush, the 

 most northern station, during the same year, was 49°*lj and 

 that at Castletownsend, the most southern, 53°* 1. The excess 

 of temperature of the sea over that of the air appears thus 

 greater than the greatest diiFerence of temperature which could 

 arise between two stations as a consequence of their difference 

 of latitude. 



On comparing the mean annual temperatures of the sixteen 

 stations where obsei-vations were made in 1851, I immediately 

 saw that the following approximately isothermal groups could 

 be formed. 



The remaining two stations, Donaghadee and Portarlington, 

 * Trans. Royal Irish Academy, vol. xxii. p. 411. 



