274 Mr Harker, Magnetic Disturbances in the Isle of Skye. 



less a definite resultant force sensible, with diminishing effect, to 

 considerable distances. Without multiplying examples, it may be 

 stated generally that this statement is borne out at numerous 

 other localities examined in a more cursory way. On those ridges 

 in the Cuillins especially which trend approximately north and 

 south, and culminate in marked summits, results showing con- 

 siderable regularity were obtained, so long as subordinate centres 

 of local disturbance residing in minor prominences were avoided. 

 Such east and west ridges as I have examined (Sgurr Dearg, 

 Sgurr nan Gobhar, and others) showed considerable deflections 

 varying from point to point and not easily reduced to any 

 semblance of order ; a fact perhaps attributable to the rough 

 profile of these ridges, presenting as they do numerous crags 

 which are centres of more or less strong local disturbance. 



My observations, taken on most of the peaks and ridges of the 

 Cuillins, though numerous, were, as already intimated, of a very 

 rough kind. They are sufficient, in my opinion, to demonstrate 

 that magnetic disturbances, gradually varying from place to place, 

 and of such magnitude as, in favourable circumstances, to be 

 detected by the compass to distances of a mile or two miles, stand 

 in relation to summits composed of highly magnetic rocks. Any 

 attempt to specify the nature of the relation must be based on a 

 much more thorough survey conducted with instruments of pre- 

 cision. The general rule on north and south ridges seems to be 

 that the deflections of the needle from the normal magnetic 



SCALE OF Y A RDS. 



Fig. 3. Behaviour of the compass needle on part of the summit-ridge of Sgurr 

 na Banachdich. The observations are marked, as before, on a ground-plan, and a 

 longitudinal profile of the ridge is added. The numbers give the deflections from 

 the normal magnetic meridian (N. 21° W.). 



meridian are in opposite directions on opposite sides of the 

 summit, and diminish in absolute magnitude with distance from 

 the summit. Sometimes the deflections are negative to the north 

 of the summit and positive to the south ; sometimes the reverse. 



