1911-12.] Transverse Induction Changes in Demagnetised Iron. 309 
now proceeds in the usual way by reversals decreasing to zero. As the 
value of — H x on the first reversal is taken less, the residual magnetisation 
becomes greater and vice versa. This method supplies a wide range of 
stable residual magnetisation more nearly approximating to the less com- 
plex seolotropy of complete demagnetisation by reversals, and to a con- 
dition such that the theoretical assumption referred to immediately above 
may be more nearly fulfilled. 
Partially Demagnetised Iron. 
(1) Experimental. 
In figs. 9 and 10 the dotted curves reproduced from fig. 4 show the 
transverse effects typical of complete demagnetisation by reversals when 
the calculated angle $ = 71 3 6. The arrows now represent not only the 
orientation of the demagnetising angle 0 as formerly, but the polarity 
of the residual magnetisation due to partial demagnetisation. If it be 
arranged that the residual magnetisation has a component coinciding 
with the field H c subsequently applied, the continuous approximately 
symmetrical curves of fig. 9 are obtained. If, on the other hand, it be 
arranged that the residual magnetisation has a component opposite to 
the field H c , the continuous curves of fig. 10, likewise symmetrical in the 
four quadrants, are the result. 
These results are quite distinct and indicate the departure of the 
transverse induction curves from those of complete demagnetisation for 
the same angle 0 when the residual magnetisation is small. 
The above experiments are typical of many others for the same 
demagnetisation angle of 0 = 71°*6, throughout a wide range of residual 
magnetisation between B = 100 and 10,000 in C.G.S. units. The curves 
are plotted in fig. 11, the orientation and polarity of the residual 
magnetisation being indicated by the arrows. Those on the right are 
the average of four practically symmetrical curves obtained under the 
conditions already described for fig. 9. Those on the left are the average 
of four practically symmetrical curves obtained under the conditions 
already described for fig. 10. In both cases the orientation of 0 is right- 
handed and the polarity of the residual magnetisation positive, but a 
component coincides with or directly opposes the subsequent field according 
as H c is positive (curves on the right) or negative (curves on the left). 
Fig. 12 gives the results of another set of experiments obtained in the 
same way when the demagnetisation angle d=18°*4, the calculated com- 
plementary angle. 
