"Want some advice, Mart. I'd thought of setting up three or four courses of five-ply screen on the board--a detector screen on the outside of each course, next to it a repeller, then a full-coverage ether-ray screen, then a zone of force, and a full-coverage fifth-order ray-screen as a liner. Then, with them all set up on the board, but not out, throw out a wide detector. That detector would react upon the board at impact with anything hostile, and automatically throw out the courses it found necessary." "That sounds like ample protection, but I am not enough of a ray-specialist to pass an opinion. Upon what point are you doubtful?" "About leaving them on the board. The only trouble is that the reaction isn't absolutely instantaneous. Even fifth-order rays would require a millionth of a second or so to set the courses. Now if they were using ether waves, 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!"