AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
89 
these curves would seem to show critical points at the 6th, 8th, and 12th kilogs., but 
as the effect on the specific resistance of this metal was found to be very great in 
comparison with that of the other substances, it was evident that the critical points as 
understood to mean points of sudden increase of length compared with the load 
producing it could not safely be deduced from the curve showing the total alteration 
of resistance. The critical points have therefore been deduced from direct observa¬ 
tions of the permanent increase of length produced by each load, and the results of 
these observations are shown in the curve of Table XI. This curve has its abscissae 
representing the permanent increase of length on a scale of *625 millim. of increase of 
length to the millimetre and its ordinates the load in kilogrammes on a scale of '2 kilog. 
to the millimetre. From the observations of increase of length the first critical point 
was determined to be at the load 2200 kilogs. per square centimetre and the second at 
the load 3100 kilogs. per square centimetre. 
Table XI.—Total permanent increase of length produced by longitudinal traction, 
The Influence of Time on the Amount of Permanent Increase of Resistance 
or of Length which can be Produced by Longitudinal Stress. 
It is well known to all who have made investigations in the subject of elasticity, that 
the permanent increase of length which can be produced by a given amount of longi¬ 
tudinal stress depends largely upon the time during which the stress is allowed to act, 
MDCCC LXXXIII. 
N 
