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In examining the results of some of the experiments upon the 

 effects of single masses of protecting metal on the sheeting, the 

 author observed, that in some cases the corrosion seemed to increase 

 \vith the distance from the protector. It became, therefore, neces- 

 sary to investigate this circumstance, and to ascertain the extent of 

 the diminution of electrical action in instances of imperfect or irre- 

 gular conducting surfaces. Sir Humphry details several experiments 

 in illustration of this inquiry, which prove that any diminution of 

 protecting effect at a distance does not depend upon the nature of 

 the metallic, but of the imperfect or fluid conductor. His experi- 

 ments upon perfect and imperfect conductors led him to another in- 

 quiry, important in its practical relations, respecting the nature of 

 the contact between the copper and the preserving metal. He found 

 the protecting action prevented by the thinnest stratum of air, or the 

 finest leaf of talc or dry paper ; but the ordinary coating of rust, or 

 a thin piece of moistened paper, did not impair it. 



After some experimental details respecting the electro-chemical 

 powers of metals in solutions excluded from air, Sir Humphry con- 

 cludes his paper with practical inferences and theoretical elucidations 

 arising out of its general details. Finding that in certain cases of 

 imperfect connexion, the influence of the protector was weakened 

 by distance, the author proposed that when ships with old sheathing 

 were to be protected, a greater proportion of iron should be used, 

 and if possible more distributed. The advantage of this plan was 

 strikingly shown in the Semerang, which had been coppered in In- 

 dia in the year 1821, and came into dock, in the spring of 1824, 

 covered with rust, weeds, and zoophytes ; she was protected by four 

 masses of iron, equal in surface to about one 80th of the copper, two 

 of which were near the stern, and two on the bows. She made a 

 voyage to Nova Scotia, and returned in January 1 825 ; not, as was 

 falsely reported, covered with weeds and barnacles, but remarkably 

 clean and in good condition. After citing other instances of the 

 perfect efficiency of the protectors, and adverting to the relative pro- 

 portion which, in different circumstances, they ought to bear to the 

 sheathing of the vessel, and to the most advantageous methods of 

 applying them, the author concludes by observing upon the import- 

 ance of selecting perfectly pure copper for the sheathing ; of apply- 

 ing it smoothly and equably ; and of using for its attachment nails 

 of pure copper, and not of mixed metal. 



On the Magnetism of Iron arising from its Rotation. By Samuel Hun- 

 ter Christie, Esq. M.A. of Trinity College, Cambridge ; Fellow of the 

 Cambridge Philosophical Society ; of the Royal Military Academy. 

 Communicated April 20, 1825, by J. F. W. Herschel, Esq. Sec. R.S. 

 Read May 12, 1825. [Phil. Trans. 1825, p. 347.] 



The effects observed and described in this paper, although minute 

 in themselves, appear, in the author's opinion, to point out a species 

 of magnetic action not hitheito described. It had long been well 



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