96 Dr. Mac Culloch's Shtcb of the 



that may be conceived to be placed. This discordancy of position 

 is still more remarkable in the several parts of a neighbouring line 

 running on the E. by N. rhumb, and proves clearly that several 

 magnetic bodies exert their influence in producing the disturbance 

 which is there visible. Were it necessary to confirm this by any 

 other observation, it would be fully proved by its deviation at a 

 distant point situated near the N.W. part of the circle, where its 

 position is such as to be evidently produced by some magnet un- 

 connected with those which cause the great irregularities crowded 

 together in the two places immediately before described. If I 

 understand rightly the account which Humboldt has given of the 

 affection of the needle by the hill of serpentine which he describes, 

 it would appear that the whole rock consisted of a single magnet 

 acting with great regularity on the needle. But in this case it is 

 plain that its deviations from the true meridian are the consequences 

 of the actions of several magnetic bodies dispersed over the summit 

 of the hill, from the intricacy of whose combined influences it will 

 evidently be impossible to determine the precise position or extent 

 of any of them. It is probable that the meridians of all these and 

 similar magnets occurring in the basaltic rocks, or in other rocks, 

 are coincident with the magnetic meridian, and that they acquire 

 this virtue as masses of iron are often known to do by long 

 continued rest in favourable positions, combined probably with 

 circumstances of which we are as yet doomed to remain in 

 ignorance, little acquainted as we are with the history and causes 

 of this obscure power. But I need not dwell longer on this 

 particular example, since in a paper on Glen Tilt, which will be 

 found in the present volume, I have entered at some length into the 

 general question. 



