The operator brought one and attaching the wires from the crystal to the instrument Mr. Henderson told them to watch the needle. Then, turning the knob on the frame and thus twisting it slightly, he brought a strain upon the crystal and instantly the needle of the voltmeter soared upward to 500.
“Jehoshaphat!” cried Frank. “That beats all yet!”
“I’ll say it does!” agreed Rawlins.
“But, why have you never told us about them before?” asked Tom.
“Simply forgot them,” replied Mr. Henderson. “I never made use of them and had merely seen their wonders demonstrated out at the Bell laboratories when I was inspector there. Thought them remarkable but of no practical value at the time, although I knew later they were used as submarine detectors and for deep-seas sounding. I can see now, however, how useful they will prove. What are you boys intending to do with them?”
“Well, we hadn’t exactly decided yet,” replied Tom, “but we thought the fellows that had this sub probably used them in receiving undersea radio and we were going to rig up something of the same sort.”
“I expect they did use them,” agreed Mr. Henderson, “and you should be able to arrange a set with them. Does Bancroft here know how those submarine detectors were arranged?”
“Well, not exactly, Sir,” replied the operator, “but I think I can manage after a bit of experimenting, Sir. That is, with the young gentlemen’s help.”
“Very well, go to it,” replied Mr. Henderson, “but you’ll find they’re doing it with your help if you don’t watch out. I’ll wager they can teach you a lot about radio.”
But both Bancroft and the boys found it a far more difficult matter to rig up a detector than they had imagined.