124 EIGHTH REPORT 1838. 



points to fall to the south of the line of 71°, contrasted with and 

 counterbalanced by an opposite tendency of the points furnished 

 for the same line on the east of Ireland*. A more extensive 

 research is necessary to determine whether, by multiplying the 

 number of stations in these localities, this apparent irregularity 

 would disappear, or whether the observations referred to truly 

 represent what may be termed a district anomaly. Whilst, 

 however, on minute examination the eye may rest on single 

 stations, or on groups, which present examples of the slight 

 irregularities here referred to, it cannot fail, on the general 

 aspect of the map, to be struck by the absence of any important 

 unsymmetrical inflections, and by the obvious general systematic 

 arrangement of the terrestrial magnetism indicated by the lines. 

 Here, as elsewhere, they present the features of the general 

 magnetic system ; the effects of local and partial disturbance 

 being indeed discernible on close examination, but not being 

 found of sufficient comparative magnitude to influence the 

 general representation. 



The lines of dip as they appear on the map are slightly 

 curved, being convex towards the S.E. If the extreme points 

 of each line were connected by an arc of a great circle, the cur- 

 vature of the arc, on the projection which is here employed, 

 would be in the opposite direction to that of the isoclinal lines, 

 or the convexity would be towards the N.W. Their departure 

 from such a straight line on the surface of the globe (or their 

 difference from great circles) is greater therefore than appears 

 in this projection. 



• This apparent dislocation of the line of 71° between England and Ireland 

 was noticed by Mr. Fox in the Report of the Royal Cornwall Polytechnic So- 

 ciety for 1835. No trace of a corresponding irregularity occurs in the conti- 

 nuity of the line 72° in crossing the Irish Channel. 



I 



