PEIRCE. — ANOMALOUS MAGNETIZATION OF IRON AND STEEL. 665 



core had no shell, where the shell of soft mild steel had the diameters 

 4.45 and 3.30 ; and where the shell made of fine, soft, varnished iron 

 wires had diameters of 4.90 and 3.35 centimeters respectively. 



In the solid shell the alternating eddy currents which "Wiedemann 

 had in mind may encircle the core, but this would not be possible in 

 the core made of shellacked wire. It is evident that both shells exert 

 a strong demagnetizing effect upon the core, even while the current is 

 running in the solenoid. All the results here tabulated agree in gen- 

 eral with those quoted in the last section. In the case of the solid 

 shell, the moment of core and shell taken together will usually be re- 

 versed after certain strengths of current, but this is never the case when 

 the shell is finely divided. Figure 18 shows a typical instance. The 

 solid core is surrounded by a wire shell, and when the exciting current 

 is suddenly destroyed the core has a reversed magnetization for values 

 of H up to about 350 gausses, as is shown in curve OQR. The whole 

 flux through the combination of core and shell as indicated by the 

 curve OWV is never negative, though for high excitations, when the 

 flux through the core is strongly positive, the flux through the shell 

 itself may be small. In one case under an exceedingly high excitation, 

 the line corresponding to OQR bent down again something like the 

 curves of Figure 13, but the observations were so difficult to manage 

 that I did not attempt to follow this out in other cases. A value of H 

 above 1700 or 1800 is hard to maintain without heating the metal and 

 the solenoid employed unduly, which masks the effect to be studied. 



The Influence of a Thick Copper Shell upon the Magnetic 

 Behavior of a Short Cylinder within It. 



Many years ago Fromme enclosed a stout piece of soft iron which 

 he was testing in a thin shell or shield of copper and was able to prove 

 that this shell did not prevent the iron from showing anomalous mag- 

 netization when the magnetizing field about it was suddenly destroyed. 



