  Much work has been done taking into account the possibility that the
gravitational {\it constant} $G$ may vary with cosmological time $t$ (or with
the cosmological scale factor $a(t)$). The same may be said about the speed of
light $c$. We present here two important remarks on these subject. These
remarks include $G(t)$ and $c(t)$ varying with time with the restriction $8 \pi
G / c^4 = \hbox{constant}$
