Gravitational Instability in Newtonian Cosmology with Varying G

Use is made of Mc\/ittiels model for Newtonian Cosrnologies with time-varying G as unperturbed Universe, in the study of linear density perturbations. A general equation for the density fluctuation is ob- 1 tained. In the case wi th nu1 l pressure and C; 5 t- (Dirac cosmological model) there results that the fluctuation density grows faster than the corresponding case for G constant. It is, however, insufficient to ex- plain the formation of Galaxies. The situation where p#O and k=O, inthe case of ideal monoatomic gas, leads only to oscillating solutions. Fi - nally, a model that "appruximates" a particular solution of Brans-Dicke theory leads to a perturbation that differs slightly from classical or relativistic ones, although insufficient for the applications abovemen- t ioned.