of Edinburgh, Session 1873-74. 337 
general method of deducing the corresponding invariants and the 
derived stress- and force-functions. It enables us to see at a glance 
the meaning of the form found for the potential energy in the 
secondary strain. The author may he allowed to add, that these 
methods have been since developed with the view of applying them 
to the problem of the elasticity of crystals, and that the results 
obtained, though dual in form, exhibit a striking coincidence with 
these now given. 
