8 AßT. 6.— S. KUSAKABE: 



6={M+<rM" }r(7 = Mrg + constaut, provided —M <zM< + M , 



whence — , > =rg = constant = 6.712 x 10 3 per gram. 

 clM ö r ö 



Or graphically, the relation between M and G may be expressed 



by a narrow parallelogram whose shorter sides are parallel to the axis 



of M and the angle contained by the adjacent sides is independent of the 



imperfection of the apparatus. The value of o determined by direct 



experiments is : 



from the first experiment, ö- 1 = , 0128 ; 



from the second experiment, <7 2 =0"0132 ; 



mean of the two, a =0*0125 ; 



Thus for instance, if the resisting mass be two kilograms, the 



couple due to the effective mass of N grams is 



either Q, l ={N— 25}rg , for the increasing couple 



or (S rf ={2V+25}rg , for the decreasing couple. 



GENERAL INVESTIGATION OF THE 

 STRESS-STRAIN RELATION. 



Two specimens, serpentine and pyroxenite, whose limits of 

 elasticity seemed to be comparatively wide, were tested by a series of 

 cycles of positive and negative couples which gradually increased in 

 their absolute amount. 



Half the difference between the maximum and minimum couples 

 in a cyclical process of the twisting and untwisting will be called the 

 Amplitude of the cycle. Half the sum of these two couples will be 

 called the Centre of the cycle. For instance, if the couple varies 

 cyclically between j+6 and j—&, then- 30 and / are called the 

 amplitude and the centre of the cycle respectively. 



In the present experiments, the centre being at origin i.e. j=o, 



