SOURCE OF ORGANIC ENERGY. 37 



more permanent groups. If the body is now left to 

 itself, it will not at once return to its original form, 

 but will only do so when the groups of the first kind 

 have broken up so often as to get back to their 

 original state of strain. 



" This view of the constitution of a solid, as con- 

 sisting of groups of molecules, some of which are in 

 different circumstances from others, also helps to 

 explain the state of the solid after a permanent 

 deformation has been given to it. In this case, 

 some of the less stable groups have broken up and 

 assumed new configurations, but it is quite possible 

 that others, more stable, may still retain their orig- 

 inal configurations, so that the form of the body is 

 determined by the equilibrium between these two 

 sets of groups ; but if, on account of rise of tem- 

 perature, increase of moisture, violent vibration, or 

 any other cause, the breaking up of the less stable 

 groups is facilitated, the more stable groups may 

 assert their sway, and tend to restore the body to 

 the shape it had before its deformation." 



According to the theory expressed in the preced- 

 ing paragraphs, it appears that the effect of a force 

 acting upon a body is greater in its molecular dis- 

 placement, and also more permanent, where all the 

 groups of molecules have a small degree of stability. 

 Thus the effects would be more permanent in a 



