1-28 



I)K. V. HOKTON ON THE MODULUS OF TORSIOXAL KKIIDITY OF 



The values of the modulus of rigidity contained in the above table were calculated 

 from the observed periods of torsional oscillation, on the assumption that the modulus 

 of rigidity of the fibre at 15 C. was 3'OOlxlO 11 dynes per sq. centim. the mean 

 value found in the first part of this research. In Diagram II. these values, and also 

 the logarithmic decrements due to the internal viscosity of the quartz fibre, are 

 plotted against the corresponding temperatures, and from the curves drawn the 

 effects of increased temperature can be readily followed. That quartz should have a 

 temperature of maximum rigidity was, of course, to be expected, seeing that at 

 ordinary laboratory temperatures its rigidity increases with rise of temperature, and 

 that it must become zero as the quartz melts. From Diagram II. it will be seen that 

 this temperature of maximum rigidity is about 880 C. 



In the experiments in the range up to 100 C. it was observed that the rigidity at 

 the ordinary temperature of the laboratory was slightly increased by heating the 

 fibre. This was also found to be the case in the experiments just described, so long 

 as the fibre was not heated above 760 C. The rigidity at the laboratory tempe- 

 rature was always diminished by heating the fibre to higher temperatures than this. 



