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We dispute not that, in some iron vessels, one or other condition may 

 exist ; but we should doubt much that, under ordinary circumstances, 

 either of these conditions do exist. In confirmation of this position, 

 I have the authority of various experiments made in her Majesty's 

 service. 



In the year 1842, so great was the inconvenience arising from the 

 deviation of the compass, that a compass department of the Admiralty 

 was established, of which the late Captain Edward Johnson was the 

 superintendent. (I am sorry to be obliged now to say the late Captain 

 Johnson, for, since the commencement of this paper, the country has 

 been deprived of the most valuable services of this gentleman.) Under 

 the superintendence of Captain Johnson, experiments were conducted 

 by some of the most accurate observers connected with her Majesty's 

 service, aided by the best of instruments. Amongst the observers referred 

 to we can number Sir James Ross, Sir John Franklin, Colonel Sabine, 

 Captains Walker, Washington, Bullock, Hornby, and forty other expe- 

 rienced officers, including, also, the names of Lieutenants Phillips, 

 Pasco, and Rigge. 



Aided by the observations of these gentlemen, the deviation of the 

 compass has been made a matter of mathematical investigation ; and 

 Mr. Archibald Smith, barrister-at-law, has constructed a set of tables, 

 by wliich the parts of deviation, resulting from permanent magnetism, 

 can be separated from that part arising from the inductive magnetism 

 that is active in the latitude in wliich the deviation is determined. 



Mr. Napier has also invented a linear method for determining the 

 same. Now, every ship in her Majesty's navy is swung for the purpose 

 of determining the deviation ; and in April last I obtained a score of 

 these tables, for the purpose of examining them by Mr. Smith's method, 

 and found that in no instance did the table show an inconsiderable 

 amount of that part of the deviation which arises from inductive 

 magnetism. Then, again, we find that actual observations have been 

 made on board the Bloodhound, Jackall, Trident, Propontis, Bosphorus, 

 &c. ; and these experiments have confirmed the conclusion at variance 

 with that arrived at by the Astronomer Royal. The experiments on 

 board of the Propontis and Bosphorus were exceedingly interesting, as 

 connected with this subject. 



In the Royal Navy, the method of the Astronomer Royal has not 

 been introduced ; but these two steamers belong to the General Screw- 

 steam Shipping Company, and had their compasses corrected on the 

 plan of the Astronomer Royal ; but, in passing to the other hemisphere, 

 their compasses were from four to five points in error. This is exactly 

 that which might be expected from reasoning on the subject. How 



