254 Proceedings of the Royal Society of Edinburgh. [Sess. 
twice as great as that due to the corresponding increase. The ( c ) curve 
shows only one maximum and one minimum in the range, and lies below 
both (a) and ( b ) till a stress of 15 kilos is passed, when it crosses (a), but 
remains below ( b ). 
Specimen II. (055 per cent. C). — Application of stress to this specimen 
gives on the whole much higher percentage values of sensitive state than 
in the case of the previous specimen, but the first maximum appears in the 
( b ) curve only at 12*5 kilos, and in the (a) curve not till 15 kilos. Both 
curves show also a minimum value within the limits of the range, and are 
rising at the end of it ; but this time too the turning-point appears later in 
the (a) curve than in the ( b ) curve. The ( b ) curve lies entirely above the 
(а) curve, and both of these are above the (c) curve, which does not at any 
point of the range rise above a value of 4 per cent. 
Specimen III. (0*8 per cent. C). — The sensitive state values for this 
specimen, fig. 4 (ii.), are much lower than those reached in either of the 
previous specimens, so far as the range examined goes, and, though there 
is a slight indication of a maximum near the beginning of the range in 
both the (a) and ( b ) curves, the values of the sensitive state remain in each 
fairly constant till a stress of 12*5 kilos is reached, after which both curves 
rise steadily. Neither has reached a maximum, however, within the limits 
of the range. The (c) curve shows only very small values, and lies below 
both the others for the whole range. 
Specimen IV. (1-2 per cent. C).— ' The (a) and (6) curves for this specimen 
show smaller values of sensitive state than any of the others. Both remain 
steady for low values of the stress, and only rise very slowly as the stress 
is increased, the (6) curve lying entirely above the (a) curve throughout the 
whole range. The sensitive state induced by the stress cycle 0-w-0 is 
negligible for all values of w from 0 to 20 kilos. 
Specimen V. (0*755 per cent. C). — This specimen shows on the whole 
more sensitive state than Specimen III., and less than Specimen II., a result 
quite to be expected if the sensitive state produced depends on the carbon 
content of the material. The form of the (6) curve is very similar to that 
of the ( b ) curve of Specimen II., but the (a) curve has its turning-points at 
lower instead of at higher stresses, as was the case with that specimen. 
The (c) curve lies throughout the range below the 2 per cent. line. 
The figures showing the effect of increasing or decreasing the stress by 
successive differences of 2*5 and 5 kilos have not been shown, as they are 
hardly of sufficient interest to merit separate discussion. As a rule, effects 
of decrease rather than of increase of stress were examined, as the ( a ) and 
(б) curves showed decrease to be the more effective in producing sensitive 
