Lindsay nodded again. "I admit it. Oh, I'll be all right."
"Well, keep it up—trying I mean. We're tinkering with the spotters and predictors and we hope to get 'em up to the point where they'll act on those lightning fast jobs."
"We'll be getting to Old London," said Lindsay. "That's next. Good thing they dispersed cities a century ago, even granting the wall shield."
"Good luck, Lindsay. And when you've covered all the mechanico-electrical angles, look for other things."
He hung up, but Lindsay pondered the last remark. What did he mean?
The ship was on its way to Old London before Lindsay called for a talk-fest.
"We don't know anything about these things excepting that they go off when we approach 'em," said Lindsay. "Has anybody any ideas?"
"Only mine," grunted Jack Grant with a half-smile. "Something triggers 'em off whenever we come close."
"Couple of hundred feet," growled Lacy, "isn't close enough to permit operation of any detector capable of registering the human body without some sort of radiation output."