Mr Blackadder's Remarks on an Optical Phenomenon, tyc. 227 



course to their compasses to regain the shore, when the man 

 in the landing-boat, looking to his compass, found it run- 

 ning round, as described by Mr Duncan. He then called to 

 the man in the next boat, whose compass was in the same 

 state, and so also were those in all the others. Mr Edmondston 

 moreover stated, although he could not speak to the fact from 

 his own knowledge, that it is always asserted and believed, 

 that, in approaching the small island of Fetlar, the compass 

 always points directly to the land, on whichever side the ap- 

 proach is made. 



Now, there cannot, I conceive, be the least question, that, 

 in any spot of this kind, where a partial terrestrial action so 

 strongly manifests itself, a considerable change would neces- 

 sarily be observed in the rate of a chronometer ; and as we 

 must look to some extraordinary cause for the anomalous re- 

 sults obtained by Mr Fisher, I think it by no means an im- 

 probable conjecture, that they might be occasioned by some 

 such partial attractions as those above described. I offer this, 

 however, merely as conjecture, and with every respect for Mr 

 Fisher's talents as an observer and mathematician. 



Art. VI. — Remarks on an Optical Phenomenon observed at 

 sunrise from the Summit of Mount JEtna. By H. H. 

 Blackadder, Esq. F. R. S. Edin. Communicated by the 

 Author. 



From the earliest ages the less familiar optical phenomena of 

 the atmosphere have attracted particular attention, less, how- 

 ever, from their grandeur or beauty than from their supposed 

 mysterious origin and incomprehensible nature. In several of 

 the most ancient writings now extant, distinct references are 

 made to some of these phenomena ; and when it is considered 

 that the human mind has a natural tendency to superstition, 

 and that it is only in the present age that the torch of science 

 has thoroughly consumed the veil which gave to these por- 

 tentous appearances almost all their previous interest, we 

 shall have but little occasion to be surprised at the wildly er- 

 roneous notions that were so long entertained regarding them. 



VOL. V. NO. II. OCTOBER 1826. Q. 



