1040 THE THEORY OF TRAN^SFORMATIONS [ch. 



method of deformation is a common one, and will often be of use 

 to us in our comparison of organic forms. 



Fig. 495. 



Fig. 496. 



(3) Our third type is the "simple shear," where the rectangular 

 coordinates become "obHque," their axes being inclined to one 

 another at a certain angle oj. Our original rectangle now becomes 

 such a figure as that of Fig. 496. The system may now be described 

 in terms of the oblique axes X, Y; or may be directly referred 

 to new rectangular coordinates f, rj by the simple transposition 

 X = i — 7) cot oj, y = r] cosec co. 



Fig. 497. 



(4) Yet another important class of deformations may be repre- 

 sented by the use of radial coordinates, in which one set of lines are 



