282 ON THE RIGIDITY 



Table II T gives the results of the observations. There is a 

 greater uniformity in the way in which the values of the 

 rigidity vary with change of tension than there was when the 

 tension was increasing, which may be ascribed in part to the 

 somewhat greater uniformity of the time intervals between 

 changing the load and determining the rigidity, and in part to a 

 greater permanence of internal structure produced by the 

 previous prolonged extension. It will be noticed (i) that the 

 values of the rigidity run through pretty much the same 

 course as they did in Table II, when the tension was being 

 increased, though the final values of Table III, in the case of 

 the static rigidity for the greater angle of torsion and in the 

 case of the kinetic rigidity for the greater angles of oscillation, 

 are less than the initial values of Table II, and (2) that the 

 minimum point is given not only by the kinetic results for the 

 amplitudes 180 and 90, but also by the static results, which 

 shows that the occuri'ence of the minimum point is not due to 

 a defect peculiar to the kinetic method. 



To see what effect the time interval between the putting on 

 of the load and the finding of the rigidity, had on the rigidity, a 

 new cord was experimented with in the following manner: A 

 weight having been put on the cord, the rigidity was deter- 

 mined both immediately afterwards and after the lapse of certain 

 intervals of time. Then nnother weight was added and the pre- 

 vious process repeated. Owing to lack of time, only the kinetic 

 method was used. Table IV gives the results. 



