Barrett — On the Physical Properties of Manganese Steel. 371 



when alloyed with steel, we are led into speculation as to the nature 

 of magnetism, and why chemical union should destroy the mag- 

 netic state. Manganese steel has about the same magnetic suscep- 

 tibility as ferric oxide ; German silver, in like manner, which is an 

 alloy of brass with the magnetic metal nickel, is itself magnetically 

 inert. Why is this ? Do the molecules of manganese insulate the 

 imaginary Amperian currents in the iron, and so prevent the mole- 

 cular movement which invariably accompanies the act of magneti- 

 sation ? But if so, how ? The electric resistance of manganese 

 steel, as a whole, is scarcely 8 times less than iron, but the magnetic 

 power is upwards of 300 times less. 



These experiments have also a practical as well as a theoretic 

 interest. From its high tenacity and negative magnetic properties, 

 manganese steel is eminently adapted for the construction of those 

 parts of machines where the magnetic properties of iron or steel 

 are a serious disadvantage — such, for example, as the bed-plates of 

 dynamos. 



Moreover, as everyone knows that the deviation of the com- 

 pass on iron ships is a grave danger in navigation, more especially 

 from the fluctuating character of the sub-permanent magnetism 

 due to the hard iron and steel, the use of manganese steel for the 

 construction of iron vessels and of ironclads in the navy, and for the 

 anchors and chain cables of all vessels, suggests a simple mode of 

 returning to the magnetic safety of our wooden vessels without 

 sacrificing the advantages of iron. 1 



1 When the foregoing Paper was read, Mr. Fletcher Moore, of Kilbride Manor, 

 called attention to the fact that a manganese iron ore mine existed at Kilbride, Co. 

 Wicklow, and stated that from this ore iron had been smelted of great tenacity and 

 high quality. 



2 2 



