304 POPULAR LECTURES AND ADDRESSES. 



prevent me from more than very slightly touching 

 on it in the present article. 



The magnetism of a ship's iron is a very 

 variable property, and it is almost as difficult to 

 classify and describe it in words as it is to correct 

 its effect on the compass. It may be imagined 

 to consist of two constituents : one permanent ; 

 the other transient, because dependent on transient 

 inductive influences. But the " permanent mag- 

 netism " is not perfectly permanent, and therefore 

 it is called " sub-permanent," or it is imagined 

 as consisting of two parts, a thoroughly permanent 

 part and a sub-permanent part. Then again, 

 the " transient magnetism " is not perfectly tran- 

 sient, but is sub-permanent. If the permanent 

 magnetism were perfectly permanent, and the 

 transient magnetism perfectly transient according 

 to changes of the influence to which it is due, it 

 would be easy to apply magnets and iron in the 

 neighbourhood of the compass, so that, whatever 

 might be the position of the ship, whether upright 

 or heeling over, or in whatever part of the world 

 she might be, the needle should point in exactly 



