"Just a moment, Doctor," Burris said. He was eyeing the machine with a combination of suspicion and awe. "A while back you mentioned something about 'outside influences.' Just what, specifically, does that mean?"
With some regret, Dr. O'Connor dropped the lead. "Telepathy," he said. "By outside influences, I meant influences on the mind, such as telepathy or mind-reading of some nature."
"I see," Burris said. "You can detect a telepath with this machine."
"I'm afraid—"
"Well, some kind of a mind-reader anyhow," Burris said. "We won't quarrel about terms."
"Certainly not," Dr. O'Connor said. The smile he turned on Burris was as cold and empty as the inside of Orbital Station One. "What I meant was—if you will permit me to continue—that we cannot detect any sort of telepathy or mind-reader with this device. To be frank, I very much wish that we could; it would make everything a great deal simpler. However, the laws of psionics don't seem to operate that way."
"Well, then," Burris said, "what does the thing do?" His face wore a mask of confusion. Momentarily, Malone felt sorry for his chief. He could remember how he'd felt, himself, when that law professor had come up with a particularly baffling question in class.
"This machine," Dr. O'Connor said with authority, "detects the slight variations in mental activity that occur when a person's mind is being read."
"You mean, if my mind were being read right now—"
"Not right now," Dr. O'Connor said. "You see, the bulk of this machine is in Nevada; the structure is both too heavy and too delicate for transport. And there are other qualifications—"