Magnetization of Iron in Bulk. 631 
Comparing figs. 3 and 4, the first thing observed is that 
the magnetizing current at first rises more rapidly when the 
core is solid than when laminated, an effect predicted by 
Mr. Heaviside but not hitherto observed. This is due to the 
Fic. 5.—Calculated and Observed Coil Currents. 
1 2 3 + 5 eo e 3 9S io is vw 3 14 15 IS 17 1S 1g 
SCALE OF TIME FOR CURVEA,|I DIVISION = 2 SECOND. 
“ ” “ = 2 SECONDS. 
shielding effects of the eddy currents, the magnetizing 
influence of the coil current not reaching the central portion 
of the core immediately. As the magnetizing wave-tront 
enters, there is a double effect, the flux density in the outer 
layers increasing with the coil current, and the area magne- 
tized also increasing. The result is that the permeability of 
the core apparently increases, as shown in fig. 8. The point 
where this begins to fall suddenly indicates the cessation of 
the core currents. This takes place in about ‘3 second, the 
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