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Proceedings of the Royal Society of Edinburgh. [Sess. 
Taking maximum values of sensitive state reached in the temperature 
range chosen, we find for fall of temperature, for steel wire 15 per cent., 
for medium carbon steel 25 per cent., for hard steel 24 per cent., and for 
cast iron 21 per cent. ; while for rise of temperature, for the same four 
specimens, we have 10, 38, 22, and 13 per cent. These maximum effects 
appear, of course, at very different temperatures. 
Again, looking at the (a), (b), and (c) curves generally, we find that as a 
rule the (6) curve lies above both the (a) and (c) curves, and for lower 
temperatures the (a) curve lies above the (c) curve, while for higher tem- 
peratures the reverse is the case. That is to say, if we consider any 
given temperature, we can generally induce a greater sensitive state by 
rendering the specimen neutral at that temperature and then allowing it 
to cool than by either heating it up to that temperature and then testing, 
or by heating and then cooling before testing. Of these two methods, the 
former is likely to be the more efficacious if the temperature considered 
lies below 400° C., the latter if it lies above. 
II. Effect of Longitudinal Strain in producing Sensitive State. 
A Gray-Ross magnetometer was employed in this investigation also, 
but, as it was desired to apply longitudinal stress to the specimen while it 
was in such a position that it could be tested magnetically, a solenoid in a 
vertical instead of in a horizontal position was used, and the one-pole 
method was adopted. 
Along narrow solenoid, about 70 cm. in length, was attached vertically 
by means of a framework to the magnetometer board, so that one end 
was about 10 cm. above the level of the magnetometer needle. An oblong 
hole in the magnetometer board and in the table below it allowed the 
solenoid to pass through, and also allowed of its being moved nearer to or 
further from the needle as required. The solenoid carried, in addition to 
the ordinary coil used for magnetising the specimen, a second coil through 
which a small current could be passed to balance, within the solenoid, the 
effect of the earth’s vertical field. 
In order to fix the specimen in the solenoid in such a way that it might 
be readily removed and adjusted, and at the same time be firmly enough 
fixed not to alter its position when subjected to stress, it was screwed at 
each end into a short length of thick brass wire. Of these brass wires, one 
could be clamped firmly into position just above the upper end of the 
solenoid, while to the other was attached a strong brass hook from which 
could be hung the weights applied, so that the specimen, when in position 
