850 Proceedings of Royal Society of Edinburgh . [sess. 
When the values of H are low — about 1 C.G.S. unit — the B-H 
curves are in the following ascending order : — 
T, Th, Ah, A, C, Ch, . . . (1) 
When the values of H are taken somewhat greater than 1*8 C.G.S. 
units, the ascending sequence is as follows 
T, Ah, Th, C, Ch, A, (2) 
And when H reaches about 5 C.G.S. units, the sequence is : — 
The more important conclusions are : — 
First. Reversals of H produce opposite effects in annealed and 
demagnetised iron. In annealed iron successive repetitions of a 
magnetising force give, as is well known, “a gradually diminishing 
range of magnetic change ” (Ewing). The permeability of the 
iron is decreased. In demagnetised iron, on the other hand, one- 
half the magnetic change of induction produced by the 1st or the 
10th or the 1000th reversal is always greater than that produced 
by the first application of a given magnetising force. In other 
words, the permeability of the iron is increased. This has 
been verified over a wide range, and is true irrespective of 
whether the iron has been demagnetised by decreasing reversals 
of co-directional or transverse forces. (See (1), (2), and (3).) 
Second. To a first application of the magnetising force, and 
when the values of H are low, annealed iron is less permeable than 
iron demagnetised by a co-directional force, but more permeable 
than iron demagnetised by a transverse force. (See (1).) When 
H exceeds the value of T8 C.G.S. units, annealed iron is more 
permeable than iron demagnetised either by a co-directional or by 
a transverse force. The greater permeability of annealed iron in 
comparison with iron demagnetised by a co-directional force is 
well known (Ewing), but it does not apply when the values of H 
are low. (See (1), (2), and (3).) The B-H curves for annealed and 
co-directionally demagnetised iron cross ; that for transversely de- 
magnetised iron remains lower than both throughout a wide range. 
Third. Reversals of the magnetising force modify the 
molecular condition of annealed and demagnetised iron, so that co- 
T, C, A, 
(3) 
