1904 - 5 .] On the Magnetic Properties of Demagnetised Iron. 851 
directionally demagnetised iron remains more permeable than 
annealed (Ewing, 1885 ; Searle, 1905) and transversely demagnetised 
iron until these curves coalesce, when H approximates to 5 C.G.S. 
units. Under the same conditions of reversals, annealed iron is 
more permeable for low values of H than transversely demagnetised 
iron; but there are indications that these curves cross to some 
slight extent before all three unite, as above mentioned. (See (1), 
(2), and (3).) 
Retentivity. — Measurements have also been made on the with- 
drawal of the magnetising force after its first application. The 
curves of residual magnetisation so obtained, accentuate the 
relative differences which exist in the induction curves under the 
conditions C, T, and A of demagnetisation. The hysteresis loops, 
still to be described, also show that the same result obtains when 
the residual magnetisation is measured on the withdrawal of the 
magnetising force after it has been reversed 200 times. 
Coercive Force. — The iron was also carried through six sets of 
cycles between the positive and negative limits of B == ± 70 and 
B= ±2230. Each set consisted of three hysteresis loops plotted 
from observations recorded after the particular values of H required 
to produce the same induction for each set, under the three con- 
ditions of demagnetisation, had been reversed 200 times. It was 
found that the curves of each set of cycles cross the horizontal 
axis and each other at the same point ; and that, consequently, 
equal negative values of H are required to reduce the iron to zero 
magnetisation from equal positive values of induction, whether the 
iron had been demagnetised by a co-directional or a transverse 
force or by annealing. 
The coercive force of the iron, therefore, appears to be absolutely 
independent of the molecular condition impressed upon the iron 
by these three methods of demagnetisation. 
Hysteresis Loss. — The differences which exist between the three 
hysteresis loops for each set of cycles, having the same maximum 
values of induction, are most easily described as relative differences 
of shear. The iron being more permeable under the C h conditions, 
these loops necessarily attain to + and - maxima at lower values of 
H (see Permeability — Third), and retain a greater proportion of their 
magnetisation when H is being reduced and finally withdrawn (see 
