PEIRCE. — ANOMALOUS MAGNETIZATION OF IRON AND STEEL. 669 



As has been already explained, some of our slow breaks were made 

 continuously with the help of a specially constructed rheostat, and 

 others, sufficiently well for the purposes, by introducing, by relatively 

 small steps, a series of resistances into the circuit. This last process 

 which was not, of course, perfectly continuous, was used in the experi- 

 ment recorded in Tables XVI. and XVII. and the effect of the copper 

 in preventing any sudden change in the induction flux in the iron is 

 evident from the figures given. 



Although many complications may occur if a piece of iron or steel to 

 be tested has a magnetic bias, or has not been uniformly tempered, the 

 experiments described in this paper seem to lend support to the theory 

 that the residual moment of an originally neutral bar which has been 

 magnetized in a solenoid, is always norm al unless the current cnits 

 way to extinction oscillates to and fro. When the exciting current is 

 destroyed without oscillating in direction, even though the process be 

 finished in a small fraction of a second, the remanent magnetization 

 has the same sign as the magnetizing field. It appears that a bundle 

 of very fine soft iron wire cannot be made to show anomalous mag- 

 netism and that a thick copper shell placed over a solid bar of mag- 

 netizable metal prevents reversals of magnetism under circumstances 

 which would produce them if the shell were away. 



It seems probable that in a short, stout rod of iron or steel exposed 

 to a magnetizing field, the intensity of magnetization in the inner por- 

 tions is less than in the outer filaments and that usually when the field 

 is removed the direction of the polarization at the axis is opposite to 

 that of the polarization at the outer surface. The direction of the lines 

 at the outer surface may be normal or anomalous according to the man- 

 ner in which the exciting current comes to its end, but in any case 

 many of the lines of magnetization form closed curves wholly within 

 the metal. 



The placing of a thick iron shell either solid or constructed of fine 

 insulated wire, about a core exposed to a magnetizing field, reduces the 

 flux through the core, and, if the exciting current be reduced gradu- 

 ally to zero, the shell usually reverses the sign of the moment which 

 the core would otherwise have had. If the circuit of the exciting cur- 

 rent be suddenly broken, the residual magnetism of the core is often 

 changed in sign by the presence of the shell. A finely divided iron 

 shell never acquires anomalous magnetization when its exciting current 

 is suddenly destroyed, but such a shell acts magnetically upon either a 



