418 Effect of Temperature on Modulus of Rigidity. 



temperatures, where both the thermal agitation and the 

 increase o£ irregularly distributed molecules are very small. 

 Hence the existence of a minimum in the viscosity temper- 

 ature curve may be explained as the result of superposition 

 of the two opposite effects just referred to. 



The results of the present experiment may be summarized 

 as follows : — 



1. For thirteen different metals, both rigidity and loga- 

 rithmic decrement at ordinary and high temperatures were 

 measured. 



2. As the temperature rises, the rigidity of these metals 

 decreases according to a parabolic law. 



3. In the case of metals having low melting-points, this 

 diminution of rigidity is very rapid, tending to zero at their 

 melting-points. For metals having high melting-points, the 

 initial diminution of rigidity is small, but as the temperature 

 becomes higher, the diminution is more and more rapid. 



4. The logarithmic decrement increases with the ampli- 

 tude of oscillation ; this increase is greater as the temper- 

 ature becomes higher. The variation is partly due to the 

 amplitude of oscillation being nat sufficiently small, and 

 partly to the loss of energy through the point of suspension. 



5. The logarithmic decrement rapidly decreases with the 

 suspended weight. 



6. The logarithmic decrement of different metals increases 

 with the rise of temperature, except in the case of metals 

 having a high melting-point. in the case of the latter it 

 decreases at first, reaches a minimum, and afterwards 

 increases rapidly. 



7. In ferromagnetic substances the logarithmic decrement, 

 and also the rigidity in a somewhat less degree, are affected 

 by the magnetic transformation, in the sense that they are 

 decreased by that transformation. 



In conclusion, the writers wish to express their cordial 

 thanks to Professor K. Honda, under whose guidance the 

 present investigation was carried out. 



Physical Laboratory, 



Imperial University, 



Sendai, Japan. 

 1st July, 1920. 



