636 



MR JAMES RUSSELL ON 



The symbol (g) will therefore mean the theoretical shielding ratio regarded as the 



above function of the ratio permeability, and the symbol ((g)) the theoretical shielding 



ratio regarded as the same function of the differential permeability. Substituting the 



d 

 values given in § 5 for -5- in above formulse, we obtain for 



Shield A. (g) = -0081 ^ +1 



and for 



„ ((?)) = -0081 g| +1 



Shield B. (g) = -01 -g +1 



" (^' ) )=' 01 dH + 1 



magnetic 



§ 9. In order to assign numerical values for B/H and dB/dR, the 

 properties of the shields require to be known. Fig. iv. shows for shields A and B, first, 

 the B-H curves, in full lines, when the magnetising force He (the true force in the iron) 

 is increased by increments from zero (Table I., columns 1 and 2) ; second, the correspond- 

 ing values of the shielding ratios (g), in dash line curves (Table I., columns 6, calculated 

 from the values of B/H given in columns 5) ; and third, the corresponding values of the 

 shielding ratios ((g)), in dotted curves (Table I., columns 8, calculated from the values 

 of dB/dH given in columns 7). 



Fig. vii. on the other hand shows for shields A and B, first, the usual hysteresis 

 loops in full line curves, when the magnetising force He carries the induction B round 

 complete cycles (Table II., columns 1 and 2) ; and, second, the corresponding values of 

 the shielding ratio ((g)) in clotted curves (Table II., columns 4, calculated from the values 

 of dB/dH given in columns 3), which is obviously the only ratio available. 



When comparison falls to be made between the theoretical shielding ratio and 

 those determined experimentally, reference will be made to these tables and curves. 



The l^steresis loss may be given here, expressed in ergs per cycle per cub. cm. for 





Max Induction B. 



^JBdB. (ergs) 



Hysteretic C 



Shield A 



9600 



3500 



•0015 



Shield B 



9750 



6700 



•0028 



