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Proceedings of the Royal Society of Edinburgh. [Sess. 
these varieties of steel are very similar to those obtained for spindle steel, 
and do not, therefore, call for special comment. 
Cast Iron . — The authors now turned their attention to other magnetic 
substances. Cast iron was first tried. This material shows an effect smaller 
than that obtained with steel, though it is still considerable. In order to 
Fig. 5. Cast Iron Specimen. 
— after annealing at 900° C. 
- - after demagnetising by cyclic reversals. 
induce the state it is necessary to heat to a high temperature. Thus, for 
H = 10 c.G.S. units, the improvement in susceptibility is 24 per cent, for a 
temperature of 900° C. For a temperature of 500° C. the percentage is 
only 8, whilst heating to 200° C. produces no measurable effect. The first 
cycle removes 50 per cent, of the total improvement. The above 
diagram shows the initial and final curves obtained from a specimen cooled 
from 900° C. 
