]g ART. 6.— S. KCSAKABE: 



that some writers have taken " defect of Hooke's Law " to mean 

 " defect of perfect elasticity" which is obviously absurd. 



When other terms are not negligible, the stress-strain relation is 

 so complicated that we have not yet any established law, notwith- 

 standing the utmost endeavours of several distinguished elasticians 

 and engineers. A. F. W. Brix (1) recognised only two terms S . a 

 which followed Hooke's law and S . r for which he could discover no 

 law. G. Wertheim {2) divided the angle of torsion into two parts 

 which correspond to S a and S r respectively, but he disregarded the 

 terms corresponding to S, and S' t . AY. Wundt (3) concluded that S, 

 and not S . , was proportional to the stress that produced it ; but 

 reachad no definite conclusion as to the term S t or S' u 



A. W. Volkmann (4) found for silk and nerve, the stress-strain 

 relation to be hyperbolic, but for muscle to be elliptic. He 

 thought this relation something peculiar to organic bodies. In F. E. 

 Neumann's paper (6) , we find a consideration of set which literally 

 corresponds to the term S r . His conclusion is that the principal sets 

 can be taken as linear functions of the principal elastic strain. More 

 recently, Yoigt (6) discussed the relation between S 00 and S r for the 

 case of tending ; while James Muir (7) experimented on the recovery 

 from overstaiu which corresponds to S' h but he arrived at no quanti- 

 tative relation. 



After all, it is no easy matter to state any exact physical relation 

 between stress, strain and time-element. In the following pages, the 



(1) A. F. W. Brix. Abhandlungen über die Cohäsions- und Elasticities- Verhältnisse 

 einiger Eisendrähte ; Berlin, 1837. 



(2) G. Wertheiui. Annale de chemie et de physique. Tom. 50. 1S57, 



(3) W. Wundt. Archiv für Anatomie, Physiologie und Wiss. Medicin. Jahrgang 1857. 



(4) A. W. Volkmann. Archiv für A, P, u. s. w. herausgegeben v. C. B. Reichert und E. 

 de Bois-Reymond. Bd. I. 1859. 



(5) F. E. Neumann. Vorlesungen über die Theorie der Elasticität der festen Körper und 

 des Lichtäthers. 1885. 



(<3) Voigt. Untersuchung der Elasticitätsverhültnisse des Steinsalzes. Leipzig. 1874. 

 (7) J. Muir. Phil. Transactions. 1900. 



