, that would be lots of time to block them, but if they
_should_ happen to have fifth-order stuff it'd get here the same time
our own detector-impulse would, and it's just barely conceivable that
they might give us a nasty jolt before the defenses went out. Nope, I'm
developing a cautious streak myself now, when I take time to do it.
We've got lots of uranium, and I'm going to put one course out."

"You cannot put everything out, can you?"

"Not quite, but pretty nearly, I'll leave a hole in the ether screen to
pass visible light--no, I won't either. You folks can see just as well,
even on the direct-vision wall plates, with light heterodyned on the
fifth, so we'll close all ether bands, absolutely. All we'll have to
leave open will be the one extremely narrow band upon which our
projector is operating, and I'll protect that with a detector screen.
Also, I'm going to send out all four courses, instead of only one--then
I'll _know_ we're all right."

"Suppose they find our one band, narrow as it is? Of course, if that
were shut off automatically by the detector, we'd be safe; but would we
not be out of control?"

"Not necessarily--I see you didn't get quite all this stuff over the
educator. The other projector worked that way, on one fixed band out of
the nine thousand odd possible. But this one is an ultra-projector, an
improvement invented at the last minute. Its carrier wave can be shifted
at will from one band of the fifth order to any other one; and I'll bet
a hat that's _one_ thing the Fenachrone haven't got! Any other
suggestions?... all right, let's get busy!"

A single light, quick-acting detector was sent out ahead of four courses
of five-ply screen, then Seaton's fingers again played over the keys,
fabricating a detector screen so tenuous that it would react to nothing
weaker than a copper power bar in full operation and with so nearly
absolute zero resistance that it could be driven at the full velocity of
his ultra-projector. Then, while Crane watched the instruments closely
and while Dorothy and Margaret watched the faces of their husbands with
only mild interest, Seaton drove home the plunger that sent that
prodigious and ever-widening fan ahead of them with a velocity
unthinkable millions of times that of light. For five minutes, until
that far-flung screen had gone as far as it could be thrown by the
utmost power of the uranium bar, the two men stared at the unresponsive
instruments, then Seaton shr