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1907-8.] Sensitive State induced in Magnetic Materials. 
bring on the phenomenon in a slight degree. Several specimens heated in 
a steam coil to 100° C. showed decided indications of the “ sensitive state.” 
As the temperatures of heating are increased up to about 700° C. the effect 
becomes more and more pronounced ; but little, if any, advantage is gained 
by carrying the temperature above 700° C. 
Effect of Time. — A specimen was freshly annealed and allowed to rest 
for several days. It was then tested and gave a diagram which was 
identical with that which would have been obtained had the test followed 
immediately on the annealing. A second specimen was annealed, tested, 
demagnetised, and put aside for several days. On retesting, no trace of the 
“ sensitive state ” could be detected. 
Effect of Vibration. — A number of similar specimens, the magnetic 
quality of which had been determined, were annealed at 900° C. These 
specimens were subjected to varying amounts of mechanical vibration. 
The first specimen was held vertically with its lower end at a distance of 
1 metre from a stone slab and allowed to fall. This resulted in a consider- 
able jarring of the specimen. The remaining specimens were given several 
falls, viz. 3, 5, 7, 10, 25, and 50 respectively. 
The rods were afterwards tested, and the “ sensitive state ” was found 
to be less marked. In those specimens which received more than five falls 
the effect was reduced to less than one-half its previous value. A reduction 
of 40 per cent, was produced by a single fall. It appears to be practically 
impossible to completely remove the “ sensitive state ” by this treatment. 
Varieties of Steel employed in the Experiments. — The following five 
varieties of steel were experimented upon : (1) very mild steel, (2) spindle 
steel, (3) thick steel wire, (4) magnet steel, and (5) a special hard steel. 
[The authors hope to furnish detailed chemical analyses of these steels in 
the second part of this paper.] 
Mild Steel. — In this variety of steel the “ sensitive state,” though 
present, is but slight, there being an improvement in the susceptibility of 
about 3 per cent, for a field strength of 6 C.G.S. units. The effect is far 
from being persistent ; one cycle is sufficient to render its existence almost 
indiscernible. 
Spindle Steel. — This steel exhibits the phenomenon in a marked degree. 
After heating above the critical point, the intensity of magnetisation for a 
field of 10 C.G.S. units has acquired an increase of about 40 per cent, on its 
final value. The coercive force has also been considerably augmented by 
the treatment. One cycle removes nearly 70 per cent, of the total 
effect. 
Steel Wire, Magnet Steel, and Hard Steel. — The results obtained for 
