MAGNETIC FORCE IN IRELAND. 



207 



The station chosen for the origin of the co-ordinates is Dublin, 

 and it is obvious that there will be as many equations of condition 

 a there are other places of observation. The coefficients of these 

 equations are given in the following table. The first, second, and 

 third columns contain the place of observation, its latitude and its 

 longitude*. The numbers in the fourth and fifth columns are the 

 differences of latitude and longitude (estimated in minutes #1 lati- 

 tude) of the place of observation and Dublin, or the values of 

 (A - Ao) and (/u - ju ) cos A ; and the numbers in the three remain- 

 ing columns are the corresponding differences of dip, of horizontal 

 intensity, and of total intensity, which form the second members of 

 the equations. The dip having been observed at Dublin in each of 

 the two years (1834 and 1835), the differences of dip are obtained 

 by subtracting that belonging to the year in which the observation 

 was made at the other station. 



TABLE VII. 



* The latitudes and longitudes of some of the more important stations have been 

 kindly furnished by the officers of the Ordnance Survey. The remainder hare been 

 taken from Arrowsmith's map of Ireland. 



t Observations made in the year 1835 give Tulla 5 - 5o = + 23'7 ; Limerick, 

 5 - 5 = - 2'-l. 



