"Well, bunch," he stated, matter-of-fact, "we're on our way. We'll be this way for some time, so we might as well get used to it. Any little thing you want to talk over?" "How long will it take us to catch 'em?" asked Dorothy "Traveling this way isn't half as much fun as it is when you let us have some weight to hold us down." "Hard to tell exactly, Dottie. If we had precisely four times their acceleration and had started from the same place, we would of course overtake them in just the number of days they had the start of us, since the distance covered at any constant positive acceleration is proportional to the square of the time elapsed. However, there are several complicating factors in the actual situation. We started out not only twenty-nine days behind them, but also a matter of five hundred thousand light-years of distance. It will take us quite a while to get to their starting-point. I can't tell even that very close, as we will probably have to reduce this acceleration before we get out of the Galaxy, in order to give detectors and repellers time to act on stars and other loose impediments. Powerful as those screens are and fast as they work, there is a limit to the velocity we can use here in this crowded Galaxy. Outside it, in free space, of course we can open her up again. Then, too, our acceleration is not exactly four times theirs, only three point nine one eight six. On the other hand, we don't have to catch them to go to work on them. We can operate very nicely at five thousand light-centuries. So there you are--it'll probably be somewhere between thirty-nine and forty-one days, but it may be a day or so more or less." "How do you know they are using copper?" asked Margaret. "Maybe their scientists stored up some uranium and know how to use it." "Nope, that's out like a light. First, Mart and I saw only copper bars in their ship. Second, copper is the most efficient metal found in quantity upon their planet. Third, even if they had uranium or any metal of its class, they couldn't use it without a complete knowledge of, and ability to handle, the fourth and fifth orders of rays." "It is your opinion, then, that destroying this last Fenachrone vessel is to prove as simple a matter as did the destruction of the others?" Crane queried, pointedly. "Hm-m-m. Never thought about it from that angle at all, Mart.... You're still the ground-and-lofty thinker of the outfit, ain't you? Now that you mention it, though, we may find that the Last of the Mohicans ain't entirely toothless, at that. But say, Mart, how come I'm as wild and cock-eyed as I ever was? Rovol's a slow and thoughtful old codger, and with his accumulation of knowledge it looks like I'd be the same way."