  In the smooth scattering theory framework, we consider a pair of self-adjoint
operators $H_0$, $H$ and discuss the spectral projections of these operators
corresponding to the interval $(-\infty,\lambda)$. The purpose of the paper is
to study the spectral properties of the difference $D(\lambda)$ of these
spectral projections. We completely describe the absolutely continuous spectrum
of the operator $D(\lambda)$ in terms of the eigenvalues of the scattering
matrix $S(\lambda)$ for the operators $H_{0}$ and $H$. We also prove that the
singular continuous spectrum of the operator $D(\lambda)$ is empty.
