308 Proceedings of the Royal Irish Academy. 



As regards the correlation of the directions enumerated, in accord- 

 ance with the theory laid down in my memoir on that subject, I 

 should part from one or other of the Great Circles which are found to 

 traverse Ireland. IN'ow, as the number of coast-line Great Circles 

 traceable on the globe has not been worked out so as to bring all 

 the principal coast lines available into the system, I can only for the 

 present show the connexion existing between those Great Circles 

 which, so far, I have found to traverse Ireland, and the principal 

 lines of direction observed by me about the Bay of Dublin. 



The three Great Circles traversing Ireland, on the eastern side, so 

 far noted, are — 



The St. Lawrence Great Circle (ISTo. 12), cuts meridian 10° W. 

 in Lat. 52° 45' N., at angle of 73° 45' E. of S. 



,, Caucasus Mts. Great Circle (No. 23), cuts meridian 10° W. 

 in Lat. 52° 30' IS"., at angle of 81° 20' W. of S. 



,, W. Coast of Portugal Great Circle (l^o. 15), cuts JS"©. 23 

 G. C. in Long. 7° 2^' W., at angle of 78° S. of W. 



The "Wexford coast line (16° 23' E.) makes with the Caucasus 

 Mountains Great Circle an angle of 70° very nearly. Taking the 

 intersection of this Great Circle with the meridian 6° W. 

 at 84° E. of south, this represents 96° W. of N. 



ISow, the second principal direction occurring about ) ^ro rtyi -ry 

 the Bay of Dublin has been shown to be . . . ) ^ 



The difference therefore is 70° 08', 



a sufficiently close approximation. 



But the direction 25° 52' "VV., and the direction ) 



16° 23' E. intersect at angle of j 



42° 15'. 



As the angles of which these are means vary by more than 3°, it 

 is evident that for certain values, such as 37° E. and 3° W. (magnetic), 

 the angle of iatersection would just be 40°. 



The eastern boundary line of the granite mass of the Co. Wicklow 

 is fairly represented by the direction 30° 08' E. JSTow this direction 

 makes with the St. Lawrence Great Circle, where it passes to the 

 north of Tramore Bay, an angle of 80° very nearly. 



Taking it at 30° 08' E., 



it intersects, in the neighbourhood of Killiney Bay, 

 the coast line lying between Wicklow Head and 

 Clough Head, of which the mean direction is taken 

 at 9° 27' W. 



The angle of intersection is therefore 39° 35', 



