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PROCEEDINGS OF THE AMERICAN ACADEMY. 



Our experiences agree with his if the shell is very thin, but seem to 

 show that a thick enough copper shell will always prevent a reversal of 

 the magnetization in a soft iron core inside. The records of experi- 

 ments on two or three specimens of soft steel with shells of different 

 thicknesses will make clear the nature of the phenomena. 



Figure 18. A represents a solid core 12 centimeters long, and B, a shell 

 made of fine, soft, varnished iron wire. This combination was magnetized 

 in a long solenoid by a current gradually applied, and then this current was 

 suddenly interrupted. OWV represents the induction flux through the cen- 

 tral section of shell and core, OQR the flux through the core alone. The 

 vertical unit is 50 maxwells, the horizontal unit 100 gausses. 



Table XIV. gives some results obtained in using a mild steel cylinder 

 1.9 centimeters in diameter and 12 centimeters long, with a copper 

 shell of the same length, and with diameters of 3.80 and 2.90 centime- 

 ters. The second and third columns give the fluxes in maxwells 

 through the central cross section of the iron when the exciting current 

 has been slowly, and quickly, brought to zero. 



