  Using the formula found by Noorbala and Sepehrinia, the wave deviation in an
inhomogeneous medium with continuous variation of propagation velocity is
deduced. For electromagnetic waves (light) that propagate in the gravitational
field, the deduced deviation is identical to that calculated from General
Relativity. The method and its consequences are a good example that verifies
the Noorbala-Sepehrinia's formula as well as the mecano-optics analogy
(Hamilton's principle / principle of stationary action and Fermat's principle)
for the bodies movement in the gravitational field.
