But five years of constantly increasing, constantly expanding, constantly improving. He never forgot the day of the _Orionad_'s landing in all that five years, though there was evidence that Laura Greggor had been reprimanded by Malcolm Greggor for her actions. But Maynard remembered, and it was Joan Forbes that pinned the silver nebula on his lapels--in public as befitted a Patrol Marshal--just before he stepped aboard the _Orionad_ to take his first major command. He hoped that Laura Greggor remembered. Then the _Orionad_ sped into the sky above Sahara Base on the way to Pluto. Guy Maynard was on his way to the top. Ertene was a dim remembrance by now, and though he could almost pick out the spot of the nomad planet's present position, it occurred to him only at odd intervals. Ertene was gone. But the strength of Ertene's knowledge was serving both him and Terra, and her brief visit was not wasted. Maynard lost himself in reverie for a half hour, relaxing in the luxury of the master's office aboard the mighty _Orionad_. Then Guy's active mind asserted itself, and he called the chief technician for a conference. Senior Executive Martin Carrington entered the office and stood at attention, and Guy recalled briefly that on his first command, he had been of the same rank as his chief technician now. Then he asked Carrington to be seated. "Carrington, I've been worrying." "Worrying, sir?" "Suppose we are attacked by a sub-ship? How may we detect him?" "You are supposing that the Martians gain the secret." "I fear they will, some day. We haven't all the brains, you know." "But a Martie, sir?" "They may capture one of ours by a fluke. Then we'd all be bear-meat." "Hardly possible, sir." "Then accept it as hypothetical, Carrington. Take off from there and answer my question." "That I cannot do, sir. Frankly, I do not know." "Then listen. I have an idea; I want you to pass on its value." "I shall try, sir." "Carrington, is it possible to establish a celestial globe that is capable of giving a negative action? No, wait, I'll explain. Our present celestial globe is positive; it operates by three-dimensional fluorescence in the sphere, glowing when a positive radiation comes in from a spaceship. What I want is a negative indication: one that will glow in any location from which there comes absolutely zero radiation. Is that possible?" "Hm-m-m," mused Carrington. "Our present level of detection is based upon the maximum level of celestial radiation, which is fairly constant in all directions save Solward. Your supposed sphere would operate on the celestial radiation--with the normal globe the entire sphere would glow--and be dark everywhere except in a place where all radiation were absorbed. It would be devilishly ticklish, sir." "You follow my reasoning?"