32 



G. F. BECKER — FINITE STRAIN IX ROCKS. 



temporary distortion. In general, the circular sections of the shear ellip- 

 soid consist of different particles when the strain begins from tin <- <■ 

 which occupy the circular sections when tin; strain ends. In other 

 words, these geometrical planes sweep through a certain angle, coinciding 

 successively with all the particles in a wedge of the mass bounded by 

 limiting materia] planes. Futher more, one of the circular sections sweeps 

 in general through a different angle from that over which tin; other 

 ranges, so that the rate of movement relatively to the particles is different. 

 This difference of rate is a matter of much importance when tin; mass 

 possesses viscosity, as all real matter seems to do. 



Piguee 2. — Ra rular Sections. 



The square of broken lines is strained to the rhomb in full line?. The full lines intersecting at 

 iii center are the final axes and lines of no distortion. The broken lines intersecting at the center 

 show the positions which these same lines occupied before strain. Thelinesi m I v to , which 

 are drawn only to the outside of the s luare, indie ite the position of the fibers which at the incep- 

 tion of strain coincided with the major axis and the linos of no distortion. The ■ - mark the 



(. I 



wedges in the unstrained solid over which the geometrical planes of no distort ion sweep. For 

 displacement ixample, p. 'A. 



The range of the circular sections must therefore be determined, and 

 it is most easily discussed by examining in the unstrained mass the 

 limiting angles between which the circular sections will vary when -train 

 of assigned amount takes place. Thegeneral formulas afford the means 

 for such a determination. 



