243 
1907-8.] Sensitive State induced in Magnetic Materials. 
at 900° C., the point A corresponding to a field of 9*5 c.G.S. units. The 
magnetising field was now varied several times between the limits H = 95 
and H = 4'5. The loop B B shows the cyclic condition finally arrived at. 
It will be noticed that the magnetic quality has not suffered diminution, 
but, on the contrary, has been slightly improved. The fact that cyclic 
treatment such as that described results in a slight augmentation of the 
value of I is, of course, well known. The loops were then repeated for a 
larger variation in H, viz. from H = 9'5 to H=— 1. This treatment 
produced a diminution in the value of I, the final condition being that 
shown in the part C C of the curve. So long as the field does not fall 
below zero, the “ sensitive state ” persists, no matter how the magnetising 
field is varied. The feeble reversed, that is negative, field here employed 
has permanently diminished the susceptibility. Larger variations further 
destroyed the quality, as will be seen in the loops DD, EE, which represent 
the values obtained after the respective cyclic states had been established. 
Several tests of this nature were carried out, and all agreed in showing 
that the deterioration in quality does not begin until the magnetising field 
has been reversed. 
The gradual falling off in the magnetic quality gives initially a peculiar 
asymmetry to the curves (see fig. 2). The process of repeated cycles 
eventually results in symmetrical curves being obtained. This is well 
shown in the following table : — 
H . 
I . 
+ 11 
+ 334 
-11 
-270 
+ 11 
+ 277 
-11 
-261 
+ 11 
+ 262 
-11 
-255 
+ 11 
+ 255 
-11 
-252 
+ 11 
+ 249 
-11 
-249 
+ 11 
+ 249 
Fig. 4 exhibits the results obtained with a specimen (annealed at 
900° C.) which was first tested for field strengths up to 2 c.G.S. units,, then 
demagnetised and tested for fields up to 5 C.G.S. units. The curves show 
that whilst the many variations of field between dz 2 c.G.S. units have 
resulted in a definite reduction in susceptibility, a variation in field 
strength between wider limits will still show an effect in reducing the 
susceptibility. The cycles carried out between H = ± 2 C.G.S. units have, 
