IN CRYSTALLIZED MEDIA. 299 



cular value (2), we shall get 



- 2(> == As + Bs + Cs 



+ Is* + 2Ps 2 s 3 + 2 Q Sl s 3 



Or by substituting for s^ s 2 , s 3 , a, f?, 7' their values, given 

 by system (3), continuing to neglect quantities of the third 

 order, we get 



ay 



dv dw _ 



-3- -r -y- -J--J- + 2-J- -j- ^-j- 



dx) \dyj \dzj dy dz ^ dx dz dxdy 



T fdv dw\* Tiffdu dw\* , T fdu dv\ 2 . . 

 + L(- r +- r +M(j-+- r +N U- +-J-) ....(4). 

 \dz dy) \dz dxj \dy dx) 



Having thus the form of the function due to the internal 

 actions of the particles, we have merely to substitute it in the 

 general formula of Dynamics, and to effect the integrations by 

 parts, agreeably to the method of Lagrange. Thus, 



