Since 1937 I have been deeply impressed and really fascinated by a certain idea of Dirac. He gave in his article of 1937 arguments in favour of the hypothesis that the so-called gravitational constant K=(8π/c ²)G might be in reality not a constant, but a function of the age of the universe. Thinking in the frame work of a Friedmann cosmological model we take the curvature of space and the average density of matter to be approximately constant in the whole space, but varying with time; and in the same manner the "gravitational scalar" K may be approximately spatially constant but decreasing in time, according to Dirac, in a first approximation inversely proportional to the age of the universe. Many discussions have been caused by this idea of Dirac, but the majority of participants in these discussions were inclined to deny its possibility. But I think that all objections made against this hypothesis are at least not better than the hypothesis itself