332 ON THE METEOROLOGY OF IRELAND. 



latitude and longitude are the arithmetical means of the latitudes 

 and longitudes of the stations of observation. The resulting equa- 

 tions are thus reduced to the following : 



(a?) 4 FS (xy] = S (a*), 

 S (yf). 



For the reason already stated, I shall employ in this calculation 

 only the results obtained at the coast stations. These are, in the 

 order of latitude, Portrush, Buncrana, Donaghadee, Killybegs, 

 Killough, "Westport, Dublin, Courtown, Kilrush, Dunmore, Cahir- 

 civeen, Castletownsend. The mean latitude and longitude of these 

 stations are 53-29', and 7'39' respectively. And we find 



S (ar 2 ) = 39094, S (xy) = - 22569, Z (f) = 65811. 



Substituting and eliminating between the second and third equa- 

 tions, we obtain 



J7= -0000319 S (arf) + -0000109 S (yf) ; 

 F= -0000109 S (xt) + -0000189 S (yt). 



By these formulas the values of T, U, and F, for each month are 

 calculated. They are given in the following Table. 



The values of U and F being known, the positions of the iso- 

 thermal lines are determined. The inclination of the isothermal 

 lines to the meridian, measured from north to west, w, and the rate 

 of increase of temperature in the direction perpendicular to them, 

 W, are known by the formulas 



tan = -^, W=J(U*+ F) 2 . 



The values of u and W for the several months are given in the 

 Table. 



