104 SIXTH RErouT — 183G. 



of similar amount, nor had I read of others who had done so. 

 The weather was fine, and I had full time to assure myself that 

 there was no instrumental mistake. After completing the series 

 of four readings in each position of the needle, all of which 

 corresponded well, I removed the instrument three several 

 times to diflferent places of observation distant ten or twelve 

 yards, always obtaining the same result. The coincidence of 

 the plane of the circle with the magnetic meridian was also 

 verified by removing the compass needle to a fourth place con- 

 siderably distant. The rock was hypersthene, remarkably tra- 

 versed and intersected by trap veins, and certainly not an eli- 

 gible spot for magnetic observations. Crossing to the other 

 side of the harbour, to a spot less intersected by trap veins, 

 near where the waters from Loch Coruisk fall into the sea, the 

 needle gave the result ^2° 59'"8, which has been included in the 

 calculation, and differs only 5'*2 ft'om the general deduction. 



The lines of dip are laid down in the annexed chart agreeably 

 to the general results which have been deduced. The dip at 

 the central position in lat. 56° 27' and long. 4" 25' is 72° 17'-3, 

 and the angle which the isoclinal lines make with the meridian 

 at this station is 54° 27'. The isoclinal lines drawn in the 

 map are those of 71° 30', 72°, 72° 30', and 73°, and are at 

 distances apart of 52*15 geographical miles. 



The near accordance in the amovmt of the angle with the 

 meridian, and of the interval corresponding to half-degrees of 

 dip, with the results obtained in Ireland in the pi-eceding year, 

 is confirmatory of both as near approximations. The angle 

 with the meridian of the isoclinal lines in Ireland is 56° 48', 

 and the interval between the lines representing half-degrees of 

 dip is 50*7 geographical miles. So far the correspondence of 

 the observations of the two years and of the two countries is 

 very satisfactory. The lines of 71° 30' and 72° are the only 

 ones that are common to both countries. If these lines are 

 prolonged from the Scottish chart, they will enter Ireland to the 

 south of the corresponding lines on the Irish chart ; the line of 

 71° 30' by a geographical space equal to about 9' of dip, and 

 that of 72° by a space equal to about 8'. In other words, 

 the dip in the north-east part of Ireland, computed from the 

 Scottish observations, would be about that number of mi- 

 nutes greater than if computed from the general result of 

 the Irish observations ; and in the north-west of Scotland the 

 dip computed by the Irish results would be the same quan- 

 tity less than by the Scotch results. Campbelton, Bangor, 

 and Stranraer are frontier stations which may illustrate this. 

 The dip at Campbelton deduced from the Irish resixlts (dimi- 



