A New Model of Ferromagnetic Induction. 493 



an undecided state, as there was no other experiment which 

 gave an equally convincing demonstration of the real 

 actions. 



In drawing attention to this matter I trust it may not lead 

 to teachers abandoning the experiment, as it is now omitted 

 in some cases. As reconstructed, besides demonstrating the 

 main theoretical point, it brings into prominence the other 

 actions, and coordinates these actions with the behaviour of 

 the electrophorus and other electrostatic facts, while it also 

 draws attention to the question of leakage and surface effects 

 which are very indefinitely understood at present but which 

 are being found increasingly important. 



Instead of being tried only with a glass jar I would 

 suggest that the experiment be tried also with a high-class 

 ebonite jar, which ?fould be less fragile than paraffin, as I 

 think it would succeed if the ebonite was kept in the dark 

 in a closed glass jar with calcium chloride up to the moment 

 of use. It is difficult to speak definitely of glass, its surface 

 state varies so, but I think in most cases if the experiment 

 were tried as usual, and then the glass jar were heated to 

 100° C. and kept over calcium chloride for 20 minutes till it 

 was cold, if the experiment was then quickly made in the 

 open air, it would be found to fail from the Franklin point 

 of view, although it succeeded well in the first trial. 



LVI. A Keiv Model of Ferromagnetic Induction. By Sir J. 

 Alfred Ewing, K.C.B., F.B.S., Principal of the Uni- 

 versity of Edinburgh *. 



I HAVE lately reconsidered, in the light of whafcis now 

 known about atomic structure, the theory of induced 

 magnetism in iron and other ferromagnetic substances which 

 I put forward more than thirty years ago, and have come to 

 see that it needs substantial amendment. A new model of 

 the process of ferromagnetic induction has to take the place 

 of the model then suggested. The new model is the subject 

 of a recent communication to the Royal Society (Proc. Roy. 

 Soc. Feb. 1, 1922), but a brief account may be offered to the 

 Philosophical Magazine, in which the model of 1890 was 

 described on its first introduction -j\ 



The revised theory and the new model retain this funda- 

 mental feature, that there is in every ferromagnetic atom a 

 Weber element possessing magnetic moment and capable of 



* Communicated bv the Author. 



t Phil. Mag., 5th series, vol. xxx. p. 205 (Sept. 1890). 



