1885.] Magnetisation of Iron, Magnetisation of Metal Rods. 265 



April 23, 1885. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. " Magnetisation of Iron." By John Hopkinson, M.A., D.Sc, 

 F.R.S. Received March 30,,1885. 



(Abstract.) 



The paper contains an account of the results of experiments which 

 have been made on a considerable number of samples of iron and steel 

 of known composition, including samples of cast iron, malleable cast 

 iron, wrought iron, ordinary steels, manganese, chromium, tungsten, 

 and silicon steels. The electrical resistance and the magnetic proper- 

 ties are determined in absolute measure. Amongst the electrical re- 

 sistances the most noteworthy fact is the very high resistance of 

 cast iron, as much as ten times that of wrought iron. The fact that 

 manganese steel is almost non-magnetic is verified, and its actual 

 permeability measured. The action of manganese appears to be to 

 reduce the maximum magnetisation of steel, and in a still greater 

 ratio the residual magnetism, but not to affect the coercive force 

 materially. It is shown that the observed permeability of manganese 

 steel containing 12 per cent, of manganese would be accounted for 

 by assuming that this alloy consists of a perfectly non-magnetic 

 material, in which are scattered about one-tenth part of isolated par- 

 ticles of pure iron. Some practical applications of the results are 

 discussed. 



II. " On the Changes produced by Magnetisation in the Length 

 of Rods of Iron, Steel and Nickel." By Shelford Bidwell, 

 M.A., LL.B. Communicated by Professor Guthrie, F.R.S. 

 Received April 1, 1885. 



(Abstract.) 



. The earliest systematic experiments on the effects produced by 

 magnetisation upon the length of iron and steel bars are those of 



a 2 



