56 PROCEEDINGS OF THE AMERICAN ACADEMY. 



TABLE III — Continued. 



a oo 



A comparison between the figures given in this table and the values 

 of Z in Table II shows that, in the case of an ellipsoidal rod only 30 

 diameters long, the density of the flux of magnetic induction through 

 the metal when the exciting field is as high as 2500 gausses, is not so 

 much as one third of one per cent less than the corresponding flux 

 density for an infinitely long rod. When the ellipsoid is 50 diameters 

 long, the flux density for 2500 gausses does not differ by so much as one 

 eighth of one per cent from the flux density in an infinitely long speci- 

 men under the same excitation, and only an extremely good determina- 

 tion of B is correct within this fraction when the value of B is above 

 25000. 



It is interesting to note that if, under excitations above, say, 2500 

 gausses, we may assume the intensity of magnetization, J = kH, to be 



constant, so that B — H is constant; dB/dH is unity and f— •-777) 



increases somewhat with H. 



In the case of the Bessemer steel mentioned here, where 1^ = 

 1694, Z is .00190, for H = 5000, while Z is .00484, if H is 20000. 



Table IV gives results obtained by Mr. Coulson and myself from a 

 long series of tests upon a special brand of Norway Iron unusually 

 permeable at high excitations. 



