25 
ang. (‘ang =- 7m) H 
and the increase of declination corresponding to each geogra- 
phical mile of distance, in a direction perpendicular to this 
line, is 
Vv (M? + N®). 
<¢ It is evident then that, to obtain the values of Mand N, 
observation must give the values of the declination at three, or 
more, stations. ‘The observations of Sir James Ross were 
taken at twelve stations, well distributed throughout the 
island ; and as they were all made during the months of Octo- 
ber and November, 1838, no correction is required to reduce 
them toacommon epoch. For convenience of reference, they 
are here extracted from Colonel Sabine’s Memoir, together with 
the longitudes and latitudes of the places of observation. 
STATION. 
Valentia, . . . | 51°56’| 10°17’| 28°42’ 
Killarney, . .| 52 2 28 11 
Westport, . .| 53 48 29 9 
Limerick,. . . | 52 40 28 3 
Conky Se, 9) ese 27 44 
Markree, . . .| 54 14 29-15 
Shannon Harbour,| 53 14 3.1.28.3 
Edgeworthstown, | 53 42 : 28 8 
28 47 
26 44 
28 8 
27 35 
Londonderry, . | 54 59 
Waterford, . .| 52 15 
Armagh, . . 54 21- 
Dublin: ewe Oa. a) 
Oora-1-7 
mm OO 
«© Taking Dublin as the origin of co-ordinates, and substi- 
tuting the values of A-A,, w—p,, and d- 8,, given by this 
Table, in the equation above given, we obtain eleven equa- 
tions of condition, from which the values of M and N are:ob- 
tained by the method of least squares. They are the following: 
M=0'°690, N=0°585.. 
