RI0IDI1 i ' I BO i D II . I l. II. I ) i ')['- | ; 



'I li<' Dumerical values are: - (Specimen No« 1,. Sand bom 



There is no reason to reject either of them, lince they were measured 

 in one and the same manner under equal unrounding condit ■ 

 Nothing but the difference <>i previoui hi toi can account for the 

 cause of such an ambiguit y i" the modulus of rigidity. 



YIELDING AND RECOVERY FROM I III. 

 YIELDING. 



Attention wo« firs! drawn by W • "ht <' ' to this subject« II' 



r::t||<<| il •■ I 'inloii'i'ilio ri'l. COTltractlO ■ < 'Utlda / /" ." Il require 



certain duration ;i- well n magnitude o pear« if tlir ; 



stress be removed for a certain period« [gnace Griulio rs) , in lii i 

 periments on torsion <>ï metallic wire, recognized also the existence 

 of both id': yielding and iIj' recovery ; bul as he could not find any 

 quantitative relation, so he concluded his memoir with the following 

 question : ' : Quelle esl la fonction 'I': la ten lion el 'In ten vant 



laquelle ces alterations -'■ produisent et disparaissent ? " 



Yielding: In most rocks, the yielding i considerable. I/i 



deed, it i-: doubtful whether there is any limit \<> the elastic yielding 



<A' certain rocks, -^ lei en the twisting coupl< ifficiently 



great. In the following experiments, equal w< i put on t.h<; 



vhich gave no couple, and the readings corresponding t<> 



itate were taken. At ;i known instant, ■■> definite amounl of 

 transported from one pan to Hi'- other. Then the ; 

 ings were taken \V>\i\ instant to instant. The results of \\\<-. <::\><:n- 

 ments ■■>■ □ iri Fig. 1 1, in PL VIM. In the - two • periments, 



the effective mass was the same but with different resistii 



(1) Weber. W. '■'. Vertes hei d. Wi>.;-. / Bd. 



I. pp. 47r, 



GKalio. If emorfe delta i " '' /,; ' 



IV, 1H42. 



