There were three of the post cards. The first one was a vividly colored picture of the Capitol at Washington. It was postmarked, “Philadelphia, November 12, 2:30 P.M.” Below the picture, in a small copperplate hand, were these figures and symbols: “I-28–38-4 x 47–30-2 x 2119–8 x 65–5-3 x 29–32-11 x 40–2-9x.”
The second post card was a picture of Park Square, Boston, with the majestic figures of Lincoln and the slave in the foreground. This, too, was postmarked Philadelphia, but the date was November 13. The symbols and figures were unquestionably written by the same hand as those on the first: “II-155–19-9 x 205–2-8 x agree x 228–31-2 x present tense x 235–13-4.”
The third card was a colored reproduction of an idyllic bayou near New Orleans. Again the postmark was Philadelphia, but the date was November 14. This card contained only: “III-41–1-9 x 181–15-10 x press.”
Professor Augustus S. F. X. Van Dusen — The Thinking Machine — turned and twisted the post cards in his slender fingers while he studied them through squinting, watery, blue eyes. At last he laid them on a table beside him, and sank back into his chair, with long white fingers pressed tip to tip. He was in a receptive mood.
“Well?” he demanded abruptly.
The bearded stranger who had offered the cards for his scrutiny was gazing at the diminutive figure and the drawn, petulant face of the scientist, seemingly in mingled wonder and amusement. It was difficult for him to associate this crabbed little man with those achievements which had placed his name so high in the sciences. After a moment the visitor’s gaze wavered a little and dropped.
“My name is William C. Colgate,” he began. “Sometime since — four weeks and three days, to be exact — a diamond was stolen from my house in this city, and no trace of it has ever been found. It was one I bought uncut in South Africa five years ago, and its weight is about thirty carats. When cut I imagine it will be eighteen to twenty carats, and it is, as it stands now, worth about forty thousand dollars. You may have read something of the theft in the newspapers?”
“I never read the newspapers,” remarked The Thinking Machine.
“Well, in that event,” and Colgate smiled, “I can briefly state the facts in the case. I have for several years had in my employment a secretary, Charles Travers. He is about twenty-five years old. Within the last four or five months I have noticed a change in his manner. Where formerly he had been quiet and unassuming, he has, through evil associations I dare say, grown to be a little wild, and, I believe, has lived beyond his income. I took occasion twice to remonstrate with him. The first time he seemed contrite and repentant; the second time he grew angry, and the following day disappeared. The diamond went with him.”
“Do you know that?” demanded The Thinking Machine.
“I know it as well as one may know anything,” replied Colgate positively. “I doubt if anyone except Travers knew where I kept the jewel. Certainly my servants did not, and certainly my wife and two daughters did not. Besides my wife and daughters have been in Europe for two months. The police seem to be unable to learn anything, so I came to you.”
“Just where did you keep the jewel?”
“In a drawer of my desk,” was the reply. “Ultimately I had intended to have it cut and present it to my oldest daughter, possibly on the occasion of her marriage. Now —” Colgate waved his hand.
The Thinking Machine sat silent for several minutes. His squint eyes were turned steadily upward and several tiny lines appeared in the domelike brow. “The problem then seems to be merely one of finding your secretary,” he stated at last. “The diamond is of course so large that it would be absurd to attempt to dispose of it in its present shape. Travers is an intelligent man; we shall give him credit for realizing this. And yet if it should be cut up into smaller stones its value would dwindle to a tenth part of what it is now. Under those circumstances, would he have it cut up?”
“That is one of the questions which I should like to have answered.”
For the second time The Thinking Machine picked up and examined the three post cards. “And what have these to do with it?” he demanded.
“That’s another question I should like to have answered,” said Colgate. “I can only believe that they in someway bear on the mystery surrounding the disappearance of the gem. Perhaps they give a clue to where it is now.”
“This is Travers’s handwriting?”
“Yes.”
“The cards obviously constitute a cipher of some sort,” explained the scientist. “Were you and Travers accustomed to communicating in cipher?”
“Not at all.”
“Then why is this in cipher?” demanded The Thinking Machine belligerently. He glared at Colgate much as if he held him to blame.
Colgate shrugged his shoulders.
“Of course,” continued the scientist, “I can find out what it means. It is elementary in character, and yet I doubt if, after we know what is in it, it will be particularly illuminating. Still, giving Travers credit for intelligence, I should imagine this to be an offer to return the diamond, probably for a consideration. But why in cipher?”
Colgate did not seem to be able to add to what he had already said, and after a few minutes took his leave, with instructions from The Thinking Machine to return on the following day, after the scientist had had an opportunity to study the post cards. He called at the appointed hour.
“Have you three-volume book of any sort that you read or refer to frequently?”
For some reason Colgate seemed a little startled. It was only momentary, however. “I suppose I have several books of three volumes,” he replied.
“No particular one that your secretary would know that you read frequently?” insisted the scientist.
Again some strange impalpable expression flitted across Colgate’s face. “No,” he said after a moment.
The Thinking Machine arose. “It will be necessary then,” he said, “for me to go over your library and see if I can’t find the book to which this cipher refers.”
“Book?” asked Colgate curiously. “If the cipher has no relation to the diamond, I don’t see that —”
“Of course you don’t see!” snapped The Thinking Machine. “Come along and let me see.”
Colgate seemed a little perturbed by the suggestion. He folded his immaculate gloves over and over as he stared at the inscrutable face before him. “It would be impossible,” he said at last, “to find anything in my library just now. As I said, my wife and daughters are abroad, and during their absence I have taken occasion to have my library and one or two other rooms redecorated and refinished. All my books meanwhile are packed away, helter skelter.”
The Thinking Machine sat down again and stared at him inquiringly. “Then when your library is in order again you may call,” he said tersely. “I can do nothing until I see the books.”
“But — but —” stammered Colgate.
“Good day,” said The Thinking Machine curtly.
Colgate went away. It was not till three days later that he reappeared. If one might have judged by his manner, he had achieved something in his absence; yet when he spoke it was in the same exquisitely modulated tone of the first visit.
“The work of redecorating has been completed,” he told The Thinking Machine. “My library is again in order, and you may examine it at your leisure. If you care to go now, my carriage is at the door.”
The Thinking Machine stared at him for a moment, then picked up his hat. At the door of the Colgate mansion Colgate and the scientist were met by a graven-faced footman, who received their hats and coats in silence. Colgate conducted his guest straight into the library. It was a magnificently appointed place, reflecting in its every detail the splendid purchasing power of money. To this sheer luxury, however, The Thinking Machine was oblivious. His undivided attention was on the book shelves.
From one end of the long room to the other he walked time after time, reading the titles of the books as he passed. There were Dickens, Balzac, Kipling, Stevenson, Thackeray, Zola — all of them. Three or four times he paused to draw out a volume and examine it. Each time he replaced it without a word and continued his search. Colgate stood by, watching him curiously.
The Thinking Machine had just paused to draw out one of the Dumas books when the stolid-faced footman appeared in the door with a telegram.
“Is this for you, sir?” he asked of Colgate.
“Yes,” replied Colgate.
He drew out the yellow sheet and permitted the envelope to fall to the floor. The Thinking Machine picked it up with something like eagerness in his manner. It was directed to “William C. Colgate.” The scientist looked almost astonished as he turned again to the book shelves.
It was ten minutes later that The Thinking Machine took out three volumes together. These comprised the famous old English novel, “Ten Thousand a Year,” a rare and valuable first edition. The leaves of volume 1 fluttered through his fingers until he came to page 28. After a moment he said “Ah!” Then he went on to page 47. He studied that for a moment or more, after which he said “Ah!” once again.
“What is it?” inquired Colgate quickly.
The Thinking Machine turned his cold, squint eyes up into the eager face above him. “It is the key to the cipher,” he said.
“What is it? Read it!” commanded Colgate. His clear, alert eyes were fastened on the, to him, meaningless page. He sought vainly there something to account for the scientist’s exclamation. But he saw only words — a page of words with no apparent meaning beyond the text of the story. “What is it?” he demanded again, and there was a little glitter in his eye. “Does it say where the diamond is?”
“Considering the fact that I have seen only two words of a possible twenty or thirty, I don’t know what it says,” declared The Thinking Machine aggressively. “The best I can say now is that with the aid of these books I shall find the diamond.”
For half an hour or more the scientist was busy running through the books in an aimless sort of way. Finally he closed the third volume with a snap and stood up.
“Travers says that he will return the gem for ten thousand dollars,” he announced.
“Oh, he does, does he?” Colgate’s tone was a sneer. Again in his face The Thinking Machine read some subtle quality which brought a slight wrinkle of perplexity to his brow.
“You don’t have to pay it, you know,” he explained tartly. “I can get it without the ten thousand dollars, of course.”
“Well, get it, then!” said Colgate a little impatiently. “I want the diamond, and it is absurd to suppose that I shall pay ten thousand dollars for my own property. Come on! Let’s do what is to be done immediately.”
“I’ll do what is to be done immediately; but I will do it without your assistance,” remarked The Thinking Machine. “I shall send for you tomorrow. When you come the diamond will be in my possession. Good day.”
Colgate stared after him blankly as he went out.
The Thinking Machine was talking over the telephone with Hutchinson Hatch, reporter.
“Do you know William C. Colgate by sight?” he demanded.
“Very well,” Hatch replied.
“Is he redheaded?”
“No.”
“Good by.”
On the following morning a short advertisem............