66 



DISPLACEMENT INTERFEROMETRY BY 



The modulus thus increases definitely with the stress, except in the first 

 case; but not so much as in the case of the measurements made in triplets. 

 These were also carefully observed and appeared as follows: 



The rod, therefore, grows apparently more rigid as a result of this alternation 

 of stress, particularly at high loads. The same result is seen in the individual 

 readings of the triplets. If the last results are taken, the curve (fig. 49) 

 results. They make a series much like figure 39 for similarly shaped hard- 

 rubber rods, and the following ratio is of the same order as the above: 



= io 10 Xo.i4 



kg. /cm. 2 



With a total change of apparatus the successive increments of rigidity 

 for the same step of loading were again investigated with similar results, 

 as follows: 



37. Apparent yield within the apparatus. It remains to determine how 

 far the above apparatus may be made rigid. With such an end in view, steel 

 rods of the dimensions 



5.o3 cm. 2r = o.37 ^=0.107 cm. 2 



