XI.—ON THE VARIATION OF THE RIGIDITY OF VULCANIZED 
InDIA-RUBBER, WITH TENSION.—By THOMAS C. HEBB, 
B. A., Dalhousie College, Halifax, N. S. 
(Communicated by Prof J. G. MacGregor on the 14th 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 vulean- 
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 ; (8) 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 magnitnde 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. Sci., 10, 28, 1898-99. 
Proc. & Trans. N.S. INST. Scr, VOL. X. TRANS.—R. 
(273) 
