38$ Lieut. Mudge on the Magnetic Influence of the 
ceding article before the public, and from whom I have received 
the following communication. 
44 Dear Sir, August 14. 18$1. 
“ The observations you have made on the magnetic power of 
the islands of St Mayo and the Great Salvage, are, I think, 
highly curious, and should be made public, as it may draw the 
attention of other observers to similar cases, which are doubtless 
frequently to be met with in different parts of the globe. The 
following remarkable instance of a like action, at a considerable 
depth under water, I learned last year from Mr Duncan, master 
attendant in his Majesty’s dock-yard Chatham. 
44 This gentleman, who has always paid great attention to the 
phenomena of the needle, informed me that, in the year 1791, 
while he commanded a vessel (the Beaver) belonging to the 
Hudson’s Bay Company, and while he was in search of a north- 
west passage, lie met with a very curious circumstance, the par- 
ticulars of which I extracted from his log-book, and I sent you 
a verbatim copy of my notes on the subject. 
44 On the 18th of August 1791, in Lat. 61° 5$' N., Long. 
9$° $3' W., being then about $0 leagues from land, with sound- 
ings from 60 to 65 fathoms, with blue mud, Mr Duncan found 
his azimuth compass (which he describes as an excellent instru- 
ment, by the senior Gilbert) suddenly affected in a very re- 
markable manner, the card refusing any fixed direction, re- 
volving round as if it had lost entirely its magnetic virtue. He 
immediately ordered up all his other compasses (seven in number), 
which were all affected in the same way. He then stood off 
farther from the land, and soon after his compasses resumed 
their usual action. Mr Duncan had with him a dipping needle 
furnished by the Royal Society, and it appears that the dip by 
it varied in a very short time from 78° to 86° ; the mean dip, 
by one series of observations, was 81° 40', and by another, 
83° 45'. All the above particulars, and several others, were 
noted by him at the time, and I extracted them from his log. 
44 Yours very truly, P. Barlow.” 
In the above statement relative to the survey of the Great 
Salvage, I have omitted to mention a very curious circum- 
stance, which seems still farther to demonstrate the strong mag- 
netic power of the island. The circumstance is this : when we 
