 Why is the air inside the machine not stale on the return trip like it had been on the prior trip?
[Transcriber's Note: This etext was produced from Galaxy Science Fiction February 1951. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed. There is one fact no sane man can quarrel with ... I'm not your father's ghost, even if I do look a bit like him. You will, you know, so why quibble about it? At least, you always have ... or do ... or will. And don't look at the machine out there too long—until you get used to it, you'll find it's hard on the eyes, trying to follow where the vanes go. You'll get used to it, of course, but it will take about thirty years. And naturally, since we have the same tastes, you can make the same for me as you're having. I'm you thirty years from now, or you're me. And you can look at the revenue stamp date, if you still doubt my story. It's a real wrench when a man meets himself for the first time. So I'll simply go ahead talking for half an hour or so, until you get over it. So let's begin when you get up in half an hour and come out with me. Yes, it'll be pretty obvious it must be a time machine. You've seen it, just a small little cage with two seats, a luggage compartment, and a few buttons on a dash. You'll be puzzling over what I'll tell you, and you'll be getting used to the idea that you are the man who makes atomic power practical. Jerome Boell, just a plain engineer, the man who put atomic power in every home. I snap on a green button, and everything seems to cut off around us. You can see a sort of foggy nothing surrounding the cockpit; it is probably the field that prevents passage through time from affecting us. You start to say something, but by then I'm pressing a black button, and everything outside will disappear. You are completely outside of time and space, as best you can guess how things are. Doesn't hurt, and when you pull your arm back, you're still sound and uninjured. Then it comes to you slowly that you're actually traveling in time. "Maybe it's no dimension—or it might be the fifth; if you're going to skip over the so-called fourth without traveling along it, you'd need a fifth.
 Because there is only one Jerome smoking inside the machine.
 Because the generator is working and clearing the air.  Because there is a clearer air flow now with the retrieval of the generator.  Because no one is smoking inside the machine.  Because there is only one Jerome smoking inside the machine.