Sam spelled him off during the day. By evening, they had hit the four-hundred-and-fifty-foot level. Jim took his first analysis in this hole. The chemicals were there. In greater concentration than at the same level in the previous hole.
Jim turned to Sam. "We have circuits for measuring potential differences on the lunar landscape. Could we make a reading at the bottom of this hole?"
Sam considered. "It'll take some doing, but I think we can manage it. What do you expect to find from that?"
Jim didn't dare tell him what was in his mind. "I don't know," he said. "But it might be worth trying—if there is anything living down there—"
By the following afternoon, Sam had made the necessary equipment arrangements so that potential readings could be obtained in the mass from which the chemical samples were being removed. The telemetered report was connected to a recorder that plotted the variations against a time scale.
As soon as the circuit was set up and calibrated, the recording meter showed a response. A very slow, rhythmic pulsation showed in the inked line on the paper.
Jim felt as if his breathing must have stopped for an infinite length of time. "That's what I thought we'd find," he said at last.
"What?" said Sam. "I don't understand what you're talking about. What do you think those pulsations mean?"
"Did you ever hear of an electroencephalograph?" said Jim, gravely.
"Electro—Sure, brain wave recordings. Jim! You don't think these waves—!"