290 Cilley — Fundamental Propositions, etc. 



the two points, for the flows or slips along these paths will in 

 general have been different. Moreover, often if not generally, 

 it would be very difficult to determine these flows or slips. 



As a last consideration let us note that, while the circum- 

 stances that produce a condition of primary stress and strain 

 frequently involve changes in the physical constitution of a 

 body, such as a change from isotropy to seolotropy, the intro- 

 duction of magnetism, polymorphism, and even chemical modi- 

 fications, these are incidental and not necessary accompani- 

 ments of the existence of primary stress and strain. 



We may conclude by stating that 



Primary stresses are limited and limited only (capacity for 

 physical resistance apart) to such as will satisfy the general 

 differential and surface equations of equilibrium for the case 

 of no surface tractions and bodily forces ; 



Primary strains are limited and limited only by the equa- 

 tions resulting from these through the application to them of 

 the stress-strain relations which are true for the material and 

 body tinder consideration y 



Primary stresses and strains are not determinate purely by 

 mathematics • 



True or actual stresses and strains (of which primary stresses 

 and strains are a component) are limited but limited only and 

 are not and can not be defined through the equations of the 

 theory of elasticity alone. 



