668 MR JAMES RUSSELL ON 



Second. —Repeated reversals of the circular force superposed upon a pre-existing 

 induction due to the transverse field abnormally increase the shielding ratio at the period 

 of maximum permeability due to the circular force ; but after this period is passed the 

 shielding ratio minus unity rapidly becomes proportional to the values of dB c /dH c as was 

 found to be the case under the " First " conditions. 



Third. — When upon a pre-existing induction due to the circular magnetising force 

 ascending from zero to a maximum, is superposed at each increment a given value of 

 the transverse field, the shielding ratio curves, although showing a well-marked initial 

 rise, assume throughout much lower values, and the theoretical formulae given in § 8 

 are not applicable. The permeability of the iron is increased to the circular, and lowered 

 to the transverse force, with this exception, that at low values of the former the 

 permeability of the iron to the transverse field is slightly increased. The superposition 

 of the transverse field appears to be the first step in a vibrational process, which only 

 becomes final under the " Fourth " conditions of field superposition, but which in itself is 

 not sufficient to wipe out all apparent connection between the shielding ratios and the 

 values of dB/dii, due to the circular field. It may be noted that as the transverse 

 field is increased, the maximum of each curve occurs nearer the vertical axis. 



Fourth. — When repeated reversals of the transverse field are superposed upon a 

 pre-existing induction, due to the circular force ascending from zero to a maximum, no 

 apparent connection appears to exist between the shielding ratio which descends from 

 their maximum values in the vertical axis, and the theoretical formulae of § 8. The 

 permeability of the iron is increased to the force which remains constant, viz., the 

 circular field, and reduced to the force which is being reversed, viz., the transverse 

 field. Hence the shielding ratio is also reduced, and does not bear any simple relation- 

 ship to the values either of B/H or dB/dH, due to the circular field ; but is a com- 

 plicated function of the magnetic properties of the iron, embracing permeability, the 

 phenomena associated with hysteresis and the effects of molecular vibration, all as 

 determined by the particular method of field superposition. 



Fifth. — When upon a pre-existing induction due to the transverse field the super- 

 posed circular force carries the iron in steps round a complete magnetic cycle, the 

 force which is varied increases the permeability of the iron to the constant transverse 

 field, and the maximum shielding ratios are abnormally increased in comparison with 

 the theoretical values obtained from even the high values of dBJdB. c , which prevail 

 during the superposed cycle. Although exact numerical correspondence with the 

 theoretical formula ((g)) given in § 8 could not, under the conditions as to hysteresis 

 and molecular vibrational effects, be anticipated, the connection between the experi- 

 mental shielding ratio curves and the changing values of dY$JdH. c impressed upon the 

 iron by the cyclic circular field is yet sufficiently striking. 



(c) When a longitudinal magnetising force is acting upon the iron in addition to 

 that due to the transverse field, the order and manner of field superposition affects the 

 shielding ratio to an enormous extent, and the same general relationship exists as was 



