PEIRCE. — PERMEABILITY OF A MASS OF FINE IRON PARTICLES. 91 



mine, I have used the value of iV computed by Du Bois ^ from the 

 experimental results of Ewing, Tanakadat^, and himself. 



Figure 2 shows half of a hysteresis diagram obtained by shearing 

 very slightly a diagram obtained by Mr. J. Coulson and me from a 

 column of untreated particles 50 centimeters long and 1 centimeter in 

 diameter, which weighed just over 100 grams. This diagram has all 

 the characteristics of the many others for which 1 have the materials. 



As the figure shows, B was almost exactly 2100 for an exciting field 

 of 255 gausses, and this corresponds to a value for / of only about 147. 

 When the external field was removed, the remanent value of / was 

 about 20.8 ; the coercive force, however, was comparatively large, 

 being about 16. It is evident that the exciting field would need to 

 be very strong to magnetize the column of particles approximately to 

 saturation. The subject of the saturization of masses of iron filings 

 has been discussed at length by Maurain and by Trenkle. 



The Jefferson Laboratory, 

 Harvard College. 



2 Ewing, The Philosophical Transactions ; Tanakadate, The Philosophical 

 Magazine, 1888; Du Bois, Annalen tier Physik., 1892; "The Magnetic Circuit," 

 chapter vi. For a criticism on this process, see Trenkle, 1. c. 



