"He's not here, sir. He cast off the auxiliary a moment or so ago." I _knew_! * * * * * Later, I told them. My explanation was short, for the solution was simple. Simple, once you grant that a man can possess infinite loyalty, infinite courage, in one lean and gangling frame. "Biggs saw," I said, "that there was only one way to save us all from death. Oh, he had blundered, yes, but we all blunder sometimes. But not all of us pay the penalty as willingly, as bravely, as he did. "Jupiter was upon us. Within minutes we would have crashed into the greatest of the solar planets. Only Biggs saw a way out. And that was--to make the speed of our ship _exactly_ approximate the speed of light at the moment of impact!" Dick said, "But how--" "He told us the answer. Mass-energy relationships. You know the fundamental theory of the Lorentz-Fitzgerald contraction. Objects moving in space are contracted along their major axis in direct proportion to their speed, with the limiting velocity, the speed of light, as their ultimate limit. In other words, at the precise speed of light, this ship existed in only a _unilateral_ dimension!" Hanson said, "You mean we--hurled over Jupiter?" "No, sir. _We went right through it!_ At that tremendous speed, our dimension-extension was zero. Hence it did not affect, nor was it affected in any way by, the bulk and mass of Jupiter. "It's as though an exceedingly fine wire, moving at lightning speed, were to be propelled through a cake of ice. Only in our case, the 'wire' was of zero dimension, and the cake of ice--Jupiter--did not even recognize that it had been penetrated. "But--" I shook my head. "But Mr. Biggs realized what this daring scheme meant. It meant that in addition to our size being reduced to the infinitesimal, our mass would be raised to the infinite--for that is the corollary of the contraction theory. "There had to be some way of getting us back to our normal shape and size. The only possible method was by the forcible alteration of our mass. And--Biggs adopted this method. He placed himself in the life-skiff, gave the necessary orders from there. Then, after the danger had been averted, he deliberately cast off from the _Saturn_, tossed himself away from us, a living sacrifice to the mathematical gods, that we might be safe." Todd said, "Our mass, for a moment, was infinite--but when he, however briefly, broke clear, it became _less_ than infinite, giving us a chance to cut the motors--" "That's right." Hanson's eyes were round and wild and fearful. "But then--where is he! We've got to turn around right away. Find him! We can't go back without--" I shook my head.