Lantin considered me before replying. "Such an achievement is beyond our present science," he conceded, "but it may be quite possible to the science of the future. You see my meaning? Remember, Wheeler, it is only within the last few years that our science has learned anything at all about time. Previously it was considered one of the last mysteries, never to be investigated or explained. But now, with the recent work of Einstein and Lorentz and Minkowski, we are beginning to learn something about this time. We have learned, for instance, that it is only another dimension of space itself, and that the four dimensions of any object are thus length, breadth, thickness, and _duration_. "We know now that time is not fixed and unchangeable, but relative and varying, that the time of Venus is not the time of earth, and that the time of Sirius is different from either. And remember, all of this we have learned within the last few years. "What, then, may not be learned in the next thousand years, the next ten thousand, the next million? Is it not reasonable to suggest that men will advance farther and farther in their knowledge concerning this elusive thing, time, until they finally will advance so far that they will be able to _control_ time, to travel in it at will, and thus sweep back from their own day, back to our present age? Is it not possible that men can do this, in some century to come?" "That _men_ can do this?" I repeated. "_Men_, you say, but the thing we saw was no man, Lantin. That thing, the Raider, was very far from human." "It is so," he admitted, "but that proves nothing. The Raider may be some thing of the far future, either a strange product of ages of change and evolution, or a visitor from another planet, racing through time and snatching up victims in every age and land. You remember that Cannell was seized at Angkor? And a thousand years ago, Angkor was a mighty city, and who knows but the Raider was speeding back to the days of Angkor's life and greatness, when it chanced on Cannell there? It is a strange business, Wheeler; but one thing I am certain of, and that is that the Raider does come from some time far in the future, and that it has taken Cannell back with it to that time." "But the method," I insisted, "the method of traveling through time? How is that accomplished? Cannell spoke of a theory he had concerning it. And he gave you those notes--" "I've examined those notes," Lantin said, "and rough and fragmentary as they are, I think that in them lies the secret of time-traveling. Cannell knew something of modern science, Wheeler, and the conclusions he drew concerning the Raider are significant. It was his theory that as time is the fourth dimension of matter, there is no basic reason why we can't move at will along that dimension. We can move as we wish in the other three, up-and-down, right-and-left, and back-and-forward, so why not in the fourth, that is, sooner-or-later?