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Proceedings of the Royal Society of Edinburgh. [Sess. 
give a closed hysteresis loop. A specimen was accordingly tested in this 
manner and gave the curve shown in fig. 2. 
In this test the magnetising field was increased to a maximum value of 
about 10 C.G.S. units, then reduced to — 10 C.G.S. units, and this procedure was 
repeated several times. Each cyclic alteration of the values of H reduced 
the corresponding values of I. The magnetic quality was very considerably 
reduced by the first cycle ; it was further lessened, though to a diminishing 
extent, by the subsequent cycles. For H = 10 C.G.S. units, I was ultimately 
reduced by over 20 per cent, of its original value. 
The form of the curves seemed to indicate that the deterioration in 
quality commenced on the first reversal of the field. This view was borne 
out by a test, the chief results of which are set out in fig. 3. 
The line 0 A indicates the initial I-H curve obtained after annealing 
