Randolph had helped himself to the secluded mu208 -eum, and duped the old Negro caretaker into believing he had bought the place.

Whenever the robber and his gang wanted to be alone they had sent the old man off on errands.

"How did you find the clue to Pleasanton's Bridge?" Joe asked. "You never saw the message in the bandoleer."

Smiley told them that Randolph, instead of going to town to find out about the deed, had returned to die museum through the cellar and climbed up back of the old fireplace. There he had spied on the boys and had heard them mention the bridge.

"Mr. Hardy, I really ain't got no hate against your boys," Smiley concluded. "I got to admit they're smarter'n I am."

If Smiley held no resentment, such was not the case with Baby Face. As the troopers led the two men away, hatred for the Hardys flashed in the youthful criminal's eyes.

When the men were out of sight, Frank said excitedly, "I think we're going to solve another mystery -the mystery of the lost tunnel! Follow me!"

He scrambled down the steps, climbing over the debris from the explosion. When he came to the cannon b.a.l.l.s, Frank stopped.

"Remember the message, 'Find coin in iron'? Hold the flashlight, Joe."

Frank opened his knife and scratched the corrod209 ing surface of one of the b.a.l.l.s. The rust fell away. Beneath shone a glint of gold.

Feverishly he sc.r.a.ped off more iron.

"The treasure! We've found it!"

The others gasped in amazement.

"It can't be! It can't be!" the general cried unbelievingly.

Mr. Hardy sc.r.a.ped another ball till the gold winked through. Joe did another, Chet a third.

"Grandfather's name is vindicated!" the general shouted, after they had cracked open every ball to be sure that they had found the missing treasure. "And the Centerville bank will get back its gold.

"Beauregard's heirs will be able to restore the plantation and can come back here to live. You Hardy boys turned the trick! Fenton, you're the luckiest man in the world to have such sons!"

The detective grinned. "I'm not contradicting you!" He turned to Chet. "Mr. Morton's got a son to be proud of, too. A good photographer."

Chet beamed. "I'll use my camera on our next case."

It was not the secondhand camera, however, which was to figure in the Hardys' next adventure, "The Wailing Siren Mystery."

"How'd they get the gold inside the cannon b.a.l.l.s?" Chet suddenly asked.

"They melted the gold bars in the blacksmith shop," Smith answered. "The melting point is very low, you know. Then they either made b.a.l.l.s of it and covered them with the iron sh.e.l.ls, or else cast hollow cannon b.a.l.l.s first and poured the gold in."

"And plugged up the holes," Chet said.

"Right."

Each of the Hardys and their friends lifted one oE the golden cannon b.a.l.l.s. As they carried them from the lost tunnel, the groups became jubilant. Halfway to the car, Chet said: "I feel so good, I think we ought to have a celebration."

"With atom crackers?" Frank grinned.

"Or one of Claude's dinners?" Joe asked, his eyes twinkling.

"Oh, boy!" Chet exclaimed.

Despite the weight of the cannon ball, he was the first one to reach the coupe. Never before had he gone so many hours without food!

THE END.