38 AKT. G.— S. KTJSAKABE : 



EXPLANATION OF PLATES. 



Remarks. Unit of couple=6"7l2x 10 6 c.g.s. unit; unit of twist = 1 S45 X L0~ s 



radian ; unit of time = one minute. 

 PI. I. 



Fig. 1- Preliminary experiment on Specimen No. 3„ shows great déviation 

 from Hooke's law and the existence of torsional hysteresis. 

 PI. II. 



Fins. 2 and 3. Front and side views respectively of the twisting apparatus. 

 ,, 4. Plan of the whole arrangement. 

 „ 5. Framework carrying the mirror. 

 PI. III. 



Fig. 0. Curve A. Yielding of the Support. Curve B. Twist of Specimen 

 No. 12j. This shows that the result of observation is not disturbed 

 by the yielding of the support. 

 PI. IV„. and IV f , 



FigS. ^ and 8. Effect of cyclical application of positive and negative couples 

 with their several amplitudes. They show the existence of torsional 

 hysteresis, even in the case where Hooke's law is tolerably fulfilled. 

 Specimens, No. 32 x and 8 2 . 

 PI. Y. 



pin. 9. Relation between the negative couple required to annihilate the 

 residual twist and the original couple. Deduced from the above 

 observations. 

 ,, 11a. Relation between the modulus of rigidity and the amplitude : 



Specimens No. 32j and 8 2 . 

 „ lib. Relation between the residual twist and the amplitude. 

 PI. VI. 



Fig. 10. Torsional hysteresis in Specimen No. 3 g . Showing the indehniteness 

 of the modulus of rigidity. 

 PI. VII. 



Figs. 12 and 13. On-curve and Off-curve respectively. Each series of ob- 

 servations admits of being connected by a straight line, so that 

 Hooke'i law is fulfilled. The difference of inclinations, however, 

 shows the ambiguity of the modulus of rigidity. Specimen No. 4^. 



