MAGNETIC SURVEY OF GREAT BRITAIN. 



i8d 



line than to the one to which it really belongs ; and this will 

 occur whenever, from accidental causes of any kind, the dis- 

 cordance exceeds in amount half the interval between the lines 

 which are represented. Such extreme cases are frequent in the 

 horizontal observations ; but are of very rare occurrence in the 

 statical. Of the 114 statical results, there are only five which 

 have been omitted in the graphical representation; (though of 

 course included in the table). Four of these are, Ballybunian, 

 Dingle, Gorey, and Rathdrum, all in the south of Ireland, and 

 amongst our earliest observations. The two first named were 

 my stations, and the intensity is in excess ; — the two others 

 were Mr. Lloyd's stations, and the intensity is in defect of the 

 general body of the results ; the omission of the four should 

 consequently have no effect on the position of the lines. 



The fifth observation omitted in the map is Captain Ross's 

 at Berwick, which would furnish a point for the line of 1 'Oo in a 

 geographical position which is nearer the line of 1'02. 



The evidence supplied by the collective horizontal observa- 

 tions is, however, too valuable to be dispensed with in the 

 representation. I have collected in the following Table the 

 values of the intensity derived, for the respective mean geogra- 

 phical positions, from the combined observations of each series, 

 both horizontal and statical. In the map the central stations 

 are designated thus, +, with the initial of the observer an- 

 nexed ; and the points furnished by the respective intensities 

 for the nearest adjacent line thus, ^, with H or S', according 

 as the series was horizontal or statical, and a figure is added 

 expressing the number of stations contributing to the result. 

 In Ireland the ope central station has been taken by Mr. 

 Lloyd as common to all the series, and the initials of the ob- 

 server, therefore, are transferred to the points. 



Table LXXXL 



