4 ART. 6.— S. KUSAKABE: 



the angle of torsion into two parts, i.e. the elastic part and the set 

 part ; he disregards, however, the elastic yielding. 



The experiments on torsion thus far referred to were made on 

 specimens, which were almost wholly metallic substances. Bevan (1) 

 in "Experiments on the Modulus of Torsion " has given a table of 

 the modulus of torsion for different kinds of wood. The strength 

 of stone and mortar was investigated by Bevan f2) with glue and by 

 Kondelt (3) with mortar : but they rather belong under the category 

 of adherence. 



Several distinguished elasticians have mathematically treated the 

 elastic nature of rocks — or rather, of crystals — , but the result of their 

 subtle analysis is of little use to the study of geological phenomena. 

 Quite recently, Professor H. Nagaoka (1) has published an essay, 

 containing a valuable table of the rigidity modulus of the various 

 rocks, which compose the outer coating of our planet. 



The present experiments were undertaken under the professor's 

 kind guidance, for the purpose of extending his investigations. The 

 following paper contains the results of the experiments on torsion, and 

 its principal object is to show how great the defect of Hookes law is 

 and how great hysteresis there exists in the relation of torsion to couple. 

 In mathematical part, a formula for the hysteresis-function due to 

 the elastic yielding (Elastische Nachwirkung or Weber's Effect) is 

 deduced. Lastly, as an appendix, the well-known wide difference 

 between the velocities of the tremors and those of the principal 

 schocks in an earthquake is explained, as an effect of the elastic 

 yielding of the rocks through Avhich the seismic waves are propagated. 



(1) Bevan. Phil. Transactions. 1829. 



(2) Bevan. Phil. Magazine. Vol. LXVTIL, 1826. "' 



(3) Rondelt. Traité théorique et pratique de l'Art de Bâtir. 1830-32. 



(4) H. Xagaoka. E. C. of Kocks and the velocity of the Seismic Waves. The Pub. of the 

 E. I. C. in Foreign Languages. No. 4. 1900. Phil. Mag. 1900. 



