ON THE METEOROLOGY OF IRELAND. 331 



Upon a comparison of the mean yearly temperatures of the 

 several stations, we observe that those of the inland stations are in 

 defect, as compared with the corresponding coast stations. ThQs 

 the mean temperature of Armagh (48'6) is less than that of 

 Donaghadee by 1, and less than that of Killough by 1'6. The 

 mean temperature of Markree (48'2) is less than that of Killybegs 

 by 2'6, and than that of Westport by 3'5. The mean temperatures 

 of Portarlington and Athy (47'3 and 48 0< 4) are in like manner in 

 defect, when compared with those of Dublin and Courtown, and 

 by an intermediate amount. I shall return to this subject hereafter, 

 and merely notice it at present for the purpose of observing that 

 no satisfactory conclusion can be drawn as to the dependence of 

 temperature upon geographical position, unless the inland and 

 coast stations be compared separately. 



Confining ourselves for the present to the coast stations, which 

 are the most numerous and the most widely distributed, we observe 

 that there is an increase of mean annual temperature in proceeding 

 from north to south of the island, the mean temperature of Portrush 

 and Buncrana being 49*0, and that of Dunmore, which is nearly 

 on the intermediate meridian. 51'6. Similarly there is an increase 

 of temperature in proceeding from east to west, the mean tempera- 

 ture of Killough and Dublin being 50'2, and that of Westport, 

 which is nearly on the intermediate parallel, 51 0< 7. 



But for an accurate determination of the rate of increase of 

 temperature in the two directions, it is necessary to combine the 

 results by the method of least squares. For this purpose let t 

 denote the observed mean temperature of any month, at any given 

 station ; T the probable temperature of the same month at an 

 assumed central station; and let the distances (in geographical 

 miles) of the former from the latter, measured on the meridian 

 and parallel of latitude to the north and west, respectively, be 

 denoted by y and x ; then, if V and U be the increase of tempe- 

 rature corresponding to a single mile in each direction, 



t=T+Ux+ Vy. 



There will be a similar equation for each station ; and combining 

 them by the method of least squares, we shall obtain the most 

 probable values of the unknown quantities T, U, and V. 



The simplest mode of employing this method in the present 

 instance is to take, as the arbitrary central station, that whose 



