he saw that if the two stars are near together in space, they could not stand still in face of each other, but that they must revolve in true orbits. Here was the discovery which came to take the place of the detection of the parallaxes of the fixed stars.
He had failed in one research, but he was led to grand conclusions. Was the force that these distant pairs of suns obeyed, the force of gravitation? This he could not settle, but his successors have done so. It was not till about 1827 that Savary, of the Paris Observatory, showed that one of Herschel's doubles was subjected to the law of gravitation, and thus extended the power of this law from our system to the universe at large. Herschel himself lived to see some of his double stars perform half a revolution.
Of Herschel's discoveries, Arago thinks this has "le plus d'avenir." It may well be so. The laws which govern our solar system have been extended, through his researches, to regions of unknown distance. The binary stars will afford the largest field for research into the laws which govern them, and to-
