XL Ox THE VARIATION OF THE RIGIDITY OF VULCANIZED 

 INDIA-RUBBER, WITH TENSION. BY THOMAS C. HEBB, 

 B. A., Dalhousie College, Halifax, N. S. 



f Communicated by Prof J. G. MacGregor on the lUfi May, 1900.) 



Mr. W. A. Macdonald* found in the course of experiments 

 conducted in Dalhousie College last year, that the rigidity 

 (kinetically determined) of a fresh or partially fatigued vulcan- 

 ized india-rubber cord, when subjected to increasing tension, at 

 first diminished, then reached a minimum, and finally increased ; 

 while in the case of a sufficiently fatigued cord, the minimum 

 point seemed to disappear. But owing to a doubtful mode of 

 gripping the ends of the cord, his experiments were not 

 conclusive. 



At Prof. MacGregor's suggestion, I have made the experi- 

 ments described below with the object of settling this question 

 and finding out what I could about the phenomenon. 



For this purpose I have (1) used the method of gripping the 

 cord which Mr. Macdonald employed in his last series of experi- 

 ments in order to exclude the source of error affecting his earlier 

 observations ; (2) applied the static as well as the kinetic method 

 of determining the rigidity ; (3) made experiments both on the 

 cord which Mr. Macdonald used and on fresh cords, and (4) 

 adopted modes of procedure, suggested by the results of my 

 earlier experiments, with respect to the time between the 

 loading of the cord and the determination of the rigidity, and 

 to the rnagnitn.de of the angle of torsion. 



The cords used were cylindrical in section, about forty 

 inches in length, and one-third of an inch in diameter. The grips 

 consisted of pieces of brass tubing of the same diameter (inside) 

 as the cord, in one end of each of which three longitudinal cuts 

 had been made. The ends of the rubber cord were drawn into 



* Proc, N. S. Inst. Set., 10, 28, 1898-99. 

 PROC. & TRANS. N. S. INST. Set., VOL. X. TRANS. R. 



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