120 



Prof. K. Honda and Mr. S. Konno on tlie 



slit IS' traces a straight line interrupted by time-marks. 

 After developing the films, the amplitude and the period of 

 oscillations can be mensured, and hence the coefficient of the 

 normal viscosity known. The maximum amplitude of oscil- 

 lations at the centre of the weight was about 2 cm. Some 

 examples of onr records are given in PL III. 



6. In order to test the formula obtained in § 4, we experi- 

 mented with copper bands of various thickness under various 

 weights. The results of experiments show that the bands of 

 different thickness give almost the same result for the 

 coefficient of normal viscosity, and that the logarithmic 

 decrement increases linearly with increasing amplitude of 

 oscillation, its magnitude depending on the materials and 

 the dimensions of the band and the loaded weight. It is 

 shown by Messrs. K. Iokibe and S. Sakai * that in the case of 

 torsional oscillations, linear relation between the logarithmic 

 decrement and the amplitude of oscillation is due on the one 

 hand to the fact that the amplitude of oscillation is not 

 sufficiently small, and on the other hand to the fact that 

 during oscillation a small fraction of energy is lost through 

 the point of suspension outwards. In the present experi- 

 ment, the linear relation between the logarithmic decrement 

 and the amplitude of oscillation is also to be attributed to 

 the same causes. These two effects become smaller and 

 smaller with the diminution of amplitude ; hence, in the 

 calculation of the coefficient of normal viscosity, the limiting 

 values of logarithmic decrement, when the amplitude of 

 oscillation becomes zero, was used. In order to minimize 

 the loss of energy through the point of suspension, the 

 bell-jar and the suspending system were constructed as stout 

 as possible. 



The dimensions of the bands are as follows : — 





Table I. 





Dimensions. 



Band 1. 



Band 2. 



Band 3. 



a (thickness) 



b (width) 



£ (length) 



0-134 cm. 

 0-380 „ 

 26-0 



0094 cm. 

 0-371 „ 

 26-0 



0049 cm. 

 0-373 „ 

 260 



The weights 1, 2, 3 are respectively 199'4, 499, and 1069 

 grams ; weight 1 is a sphere and the other two a flat 

 cylinder made of lead. 



* Phil. Mao-, loc. cit. 



