Redgrave went back to the conning-tower without replying. The only possible solution of the mystery of the deviation had suddenly dawned upon him, and a very serious solution it was. He remembered there were such things as dead suns--the derelicts of the Ocean of Space--vast, invisible orbs, lightless and lifeless, too distant from any living sun to be illumined by its rays, and yet exercising the only force left to them--the force of attraction. Might not one of these have wandered near enough to the confines of the Solar System to exert this force, a force of absolutely unknown magnitude, upon the _Astronef_? He went to the desk beside the instrument-table and plunged into a maze of mathematics, of masses and weights, angles and distances. Half an hour later he stood looking at the last symbol on the last sheet of paper with something like fear. It was the fatal _x_ which remained to satisfy the last equation, the unknown quantity which represented the unseen force that was dragging them into the outer wilderness of insterstellar space, into far-off regions from which, with the remaining force at his disposal, no return would be possible. He signalled to Murgatroyd to increase the development of the R. Force from a tenth to a fifth. Then he went to the lower saloon, where Zaidie was busy with her usual morning tidy-up. Now that the mystery was explained there was no reason to keep her in the dark. Indeed, he had given her his word that he would conceal from her no danger, however great, that might threaten them when he had once assured himself of its existence. She listened to him in silence and without a sign of fear beyond a little lifting of the eyelids and a little fading of the colour in her cheeks. "And if we can't resist this force," she said, when he had finished, "it will drag us millions--perhaps millions of millions--of miles away from our own system into outer space, and we shall either fall on the surface of this dead sun and be reduced to a puff of lighted gas in an instant, or some other body will pull us away from it, and then another away from that, and so on, and we shall wander among the stars for ever and ever until the end of time!" "If the first happens, darling, we shall die--together--without knowing it. It's the second that I'm most afraid of. The _Astronef_ may go on wandering among the stars for ever--but we have only water enough for three weeks more. Now come into the conning-tower and we'll see how things are going." As they bent their heads over the instrument-table Redgrave saw that the remorseless needle had moved two degrees more to the right. The keel of the _Astronef_, under the impulse of the R. Force, was continually turning. The pull of the invisible orb was dragging her slowly but irresistibly out of her line.