214 



ANIMAL MECHANICS. 



The perpendicular pressure acting on the elementary 

 triangle Cxy is 



The tangential strain on the element xy, is perpendicular 

 to this element, and parallel to Oz, and its vertical component 

 is 



Tds x cos (COz); 



but 



cos (COz) = 



V 



where p is the radius of curvature of the section of the surface 

 made by the plane OzC. 



Hence, finally, 



P x I 



Tds x I. 



P = 



2T 



Fig. 50. 



(36) 



In using this equa- 

 tion it must be con- 

 stantly borne in mind 

 that p is the ra- 

 dius of curvature of 

 the section passing- 

 through the perpen- 

 dicular let fall on 

 the tangent to the 

 indicatrix, and not 

 that of the section 

 passing through the 

 radius vector. 



Let xtSty, Fig. 

 50, represent this 



