  We give an estimate of the gravitational field of force exerted on a test
particle by the far galaxies, in the frame of the weak field approximation. In
virtue of Hubble's law, the action of the far matter turns out to be non
negligible, and even the dominant one. An extremely simplified cosmological
model is considered. A nonvanishing contribution is obtained only if the
discrete and fractal nature of the matter distribution is taken into account.
The force per unit mass acting on a test particle is found to be of the order
of $0.2 cH_0$, where $c$ is the speed of light and $H_0$ the present value of
Hubble's constant.
