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can we account otherwise for the fact that in this hemisphere the 

 deviation of the compass is generally west when the ship s head is west, 

 and east when the ship's head is east. The Astronomer Royal ascer- 

 tained that the permanent magnetism of the Rainbow and Ironsides was 

 such as to produce this result ; that is, that their bows were perma- 

 nently south poles, and their stems were north poles ; and he concludes, 

 therefore, that the stems of all iron vessels are north poles, and their 

 bows south. I can scarcely imagine what can be the difference in the 

 materials of iron vessels that can ensure such a result, or, rather, that 

 should render the contrary phenomenon a rare exception. There are 

 only two iron steamers in her Majesty's service, that I am aware of, 

 that are exceptions, the Onyx and the Dover. If we investigate the 

 cause that influences the poles of a ship's permanent magnetism, we 

 shall find it to be the direction of the slip on which she was built. It 

 appears that the slips on which these two ships were built had their 

 heads southward ; consequently the heads were towards the south 

 during the time that they were being built. Now, it is a well-known 

 principle in magnetism, that if a piece of hard iron be held in the 

 magnetic meridian, and stmck repeatedly with a hammer, it will 

 become magnetic, and that will be the north* pole that is directed 

 towards the north. If hammering can possibly make the inductive 

 magnetism permanent, we cannot be surprised if an iron steamer should 

 have the full amount of permanent magnetism that the materials are 

 capable of acquiring ; the rivetting of the plates being the very force 

 calculated to produce this effect. Now we have slips inclining in every 

 direction, and, consequently, we have no reason to believe that the 

 permanent magnetism is generally the same. But, if we allow that 

 the inductive magnetism has a considerable influence in determining 

 the deviation, we can account for this phenomenon by showing that, 

 generally, a greater amount of magnetic influence exists between the 

 bows and compass, than between the stern and compass. 



Having stated these views on the subject under consideration, I leave 

 it to the Society to judge, whether the greatest caution ought not to be 

 employed in connection with the compasses of iron vessels proceeding 

 to the other hemisphere. If so, is it not the duty of all who have 

 influence to promote this object ? But I would further suggest, that 



• The term north pole is here employed as it is in coDnectioa with compasses gooerally. 

 Strictly speaking in conformity with the theory of magnetism, if the north pole of the earth 

 is to be regarded as being the north pole of a magnet, that which is called the north pole of th« 

 compass should be called the south pole, because poles of different names attract each other. 

 But siuce such a nomenclature would lead to mistake with the mariner who is not versed 

 in the theor}- of magnetism, the pole of the earth and that of the magnet which attract each 

 other are allowed to be called by the same name. 



