In the meanwhile the motor boat had been repaired and was ready for service. The weather had cleared, and in the intervals of working over the mysterious paper in the box the boys, escorted by the girls, went to the place where it had been found. The hole in the sand was just as they had left it.
"The men haven"t come back to discover their loss," said Betty.
"Or, if they have, they are leaving the ground undisturbed with a view to getting a clue to the one who took the box," Allen said, with a look at Betty.
The next day a real attempt was made to decipher the code. As Allen had said, it was made up of several letters, numbers and arbitrary signs, some of them resembling Chinese characters in form.
"The thing to do," said Allen, "is to pick out the letter, number or sign that occurs most frequently. In other words, the predominating one.
And that will be E, for E is the predominating letter in any communication. Now we"ll begin."
They all had great hopes, but, alas! they were doomed to disappointment.
For either Allen"s system was wrong, or else the cipher did not follow the plan of any of the well known ones. They succeeded in deciphering it, after a fashion, but the result was a meaningless jumble of words that told them nothing. The word "treasure" did not even occur; that is, according to the translation made by Allen.
"Well, I give up," he said, with a sigh of disappointment. "I sure thought I could make something of it, but I can"t."
"Maybe Will could send it to some of his Secret Service friends,"
suggested Grace.
"Yes, I could do that," her brother a.s.sented. "Let"s let the government experts take a crack at it, Allen."
"I"m willing," a.s.sented the young lawyer.
Betty was in a corner of the big sitting room, the bay window of which gave a beautiful view of the ocean. She had the queer box in her lap, and was turning it from side to side, now and then holding it to her ear and shaking it.
"What are you doing, Betty Nelson?" asked Grace, coming in from a walk to town.
"I was just listening to see if there was any hidden mechanism in this box," answered the Little Captain. "I wonder if there"s a ruler anywhere about?" she went on.
She found a foot ruler, and with that began measuring inside and outside the box, jotting down some figures on a piece of paper.
"What"s this--a new way to work out the cipher I couldn"t solve?" asked Allen, coming in.
"Don"t talk to me for a minute, please," said Betty, puckering up her forehead.
She seemed to be adding and subtracting, and then she suddenly cried:
"I thought so! I thought so! It is the only way to account for the thickness of it."
"The thickness of what?" asked Allen.
"The bottom of that box!" went on Betty. "It has a false bottom. I"m sure of it. Look here! It is seven inches deep on the outside, and only five inches deep inside. Where are those two missing inches except in a false bottom?"
In her excitement Betty tapped on the inside of the bottom of the box with the ruler, and then a strange thing happened.
There was a clicking, springing sound, and the bottom of the iron box seemed to rise up in two parts, like the twin doors of a sidewalk elevator hatchway. The false bottom had been found, and as it swung up out of the way there was disclosed an opening in which lay a package wrapped in white tissue paper.
"Oh! Oh!" cried Betty, staring at the box "I--I"ve found it--the treasure!"
CHAPTER XIII
THE DIAMOND TREASURE
For a moment the others cl.u.s.tered around Betty like bees in a swarm, saying not a word. The girls could only gasp their astonishment as they looked over the Little Captain"s shoulder, as she sat there, holding the black box, the false bottom of which had so unexpectedly opened before their eyes.
The boys were a little more demonstrative.
"How in the world did you do it, Bet?" asked Will.
"Did you know there was some trick about the box?" demanded Roy.
"She"s been holding this back," declared Henry, nudging his sister Amy.
"And to think of all the time we wasted on that cipher!" observed Allen, reproachfully.
This seemed to galvanize Betty into speech.
"I didn"t know a thing about it!" she declared, earnestly. "I just discovered it by accident. Of course when I found there was a difference in depth between the inside and the outside of the box I began to suspect something. But I didn"t dream of--this!"
She motioned to the white package in the secret compartment--a package she had not, as yet, touched.
"But how in the world did you come to discover it, Betty dear?" asked Mollie, with wonder-distended eyes.
"It seemed to open itself," the Little Captain replied. "I just dropped the end of the ruler in the box, and it sprang open."
"You must have touched the secret catch, or spring," was Allen"s opinion.
"Let"s have a look!" proposed Will. "I always did want to see how one of those hidden mysteries worked. Pa.s.s it over, Betty!"
"Indeed, don"t you do it!" cried Mollie. "Let"s see, first, what is in that package, Betty. You said it was a treasure; didn"t you?"
"Well, that"s what I said," admitted Betty. "But it will probably be some more meaningless cipher."
"Oh, do open it!" begged Grace. "I"m all on pins and needles----"
"Thinking it may be--chocolates!" teased her brother.
She aimed a futile blow at him, which he did not even dodge.
Betty reached in and lifted the white tissue-paper package from its hiding place. It almost completely filled the s.p.a.ce. There was a rustling sound, showing that the paper had acquired no dampness by being buried under the sand in the box.
"Put it on the table," suggested Allen, removing the box from Betty"s lap. She turned to the table, near which she had been sitting, when her experiment resulted so unexpectedly. On the soft cloth she laid the paper packet.
"Now don"t breathe!" cautioned Mollie, "or the spell will be broken."