The stress components referred to the rotated axes are,

(26.5)

        
The quantities  are the increments of stresses referred to axes which rotate with the medium. It is possible to express the stresses  in terms of the stresses  by using the transformation formulas presented earlier,

(26.6)

For small angle of rotation, to the first order approximation ( , ), we have:

	(26.7a)
	(26.7b)
	(26.7c)