96 Proceedings of Royal Society of Edinburgh. [sess. 
say, the C T T conditions. The effect of repeated reversals of the 
transverse field is shown to increase the permeability of the iron to 
the force which remains constant, viz., the circular field, and, in 
virtue of the phenomena associated with hysteresis, to lower the 
permeability of the iron to the transverse field, and consequently 
also to lower the shielding ratio. 
Further, when, upon a pre-existiug induction due to the trans- 
verse field, the superposed circular field carries the iron round a 
complete cycle, the shielding ratio curves resemble the theoretical 
curves obtained from the corresponding values of dR/dK impressed 
upon the iron by the circular field. 
III. The effects of a longitudinal magnetising force acting upon 
the iron in addition to that due to the transverse field have not 
yet been fully investigated. Preliminary experiments show that in 
this case also the order and manner of field superposition largely 
determine the shielding ratios. Also that when, upon a pre- 
existing induction due to the transverse field, increments of the 
longitudinal field are superposed, the differential permeability 
appears to be the determining factor. 
{Issued separately March 31 , 1902 .) 
