670 PROCEEDINGS OF THE AMERICAN ACADEMY. 



solid or a divided core and often reverses the sign which the core would 

 have without it. 



It is difficult to make even short, stout pieces of glass-hard tool steel 

 show anomalous magnetization, and it is impossible to reverse the 

 magnetism of very long pieces of soft iron where the end effects are 

 not sensible. 



The experiments of Mr. L. A. Babbitt, as well as previous experi- 

 ments of our own, seem to show conclusively that none of the von 

 Waltenhofen effects are to be looked for in massive transformer cores 

 if these are made of fine varnished wire. I have never seen anomalous 

 magnetism in a uniformly annealed closed ring. 



It is evident that if the solenoid current in a test for anomalous 

 residual magnetism be suddenly broken, the change in the electro- 

 magnetic field in the iron is much more rapid when the core is made 

 of lengths of fine, varnished wire than when it is solid and eddy cur- 

 rents in it shield the inner filaments. Indeed, if the core be made of 

 wires of a uniform size, the average rate of change of H with the time 

 is roughly proportional to the area of one wire. If, however, the 

 circuit be suddenly closed, the change in the field in the iron caused 

 by the exciting current cannot be made instantaneous even if eddy 

 currents be wholly shut out, and the effect of dividing the core is not 

 so striking. If the magnetized particles of a piece of iron are imbedded 

 in a quasi viscous medium, the rapidity of the changes in the forces 

 acting upon the molecules should affect the magnetic properties of 

 the iron. 



My thanks are due to the Trustees of the Bache Fund of the 

 National Academy of Sciences, who have lent me some of the appara- 

 tus used in making the observations mentioned in this paper. 



The Jefferson Physical Laboratoby, 

 Cambridge, Mass. 



