As the boys got out the big crystals the regular operator’s eyes gleamed. “By Jupiter!” he exclaimed, “That’s the first time I’ve seen those since the war. We used ’em in submarine detectors you know—could hear a sub’s screw whirring three miles off.”
“Hurrah, then you know about them!” cried Tom. “I’m awfully glad you do. We only read about them and Mr. Rawlins wouldn’t believe the things we told him, so we’re going to show him.”
“Well, I don’t know such an all-fired lot either,” admitted the naval man. “But I know they worked wonders as we used ’em.”
“Let’s see,” said Tom as he examined the crystal in its metal support. “We have to connect it with our amplifier. There, that may not be right, but it’s the way I understand it. Then we connect another crystal to the amplifier. Now let’s see. They say that if this is done right and the first crystal is scratched or rubbed on something, the second one will reproduce the noise, only thousands of times louder.”
As he spoke, he gingerly touched the crystal, but nothing happened. With a puzzled look he rubbed his finger across it and still no result. Then, opening his pocket knife he scratched the crystal deeply, but still nothing occurred.
Rawlins began to laugh. “Nothing doing!” he exclaimed. “I’ll bet they’re only good for medicine.”
“I expect we haven’t got it connected properly,” said Frank. “Let’s try a different combination.”
While he spoke the two boys were busy disconnecting and rearranging the wires while Rawlins chuckled and kidded them good-naturedly.
Finally the boys had the wires connected and as Tom turned on the filament to the amplifier tubes in preparation for another trial Rawlins, who had been casually examining a bit of crystal tossed it onto the table. Instantly there was a shivering crash.
“Struck a reef!” cried Rawlins, and with frightened eyes all stood motionless, silently staring at one another and expecting each moment to feel the craft reeling or to hear excited shouts from the engine room. Was she injured? Was their cruise to end so soon? Was the submarine sinking? Such thoughts sped through the boys’ minds and each wondered how long they would stand there waiting for the order to desert their craft. But the steady throb of the engines continued. No sounds of excitement came from the engine crew. No signal from the navigator.