One ounce of radium! Within his open palm Professor Dexter held practically the world’s entire supply of that singular and seemingly inexhaustible force which was, and is, one of the greatest of all scientific riddles. So far as known there were only a few more grains in existence — four in the Curie laboratory in Paris, two in Berlin, two in St. Petersburg, one at Leland Stanford University and one in London. All the remainder was here — here in the Yarvard laboratory, a tiny mass lumped on a small piece of steel.

Gazing at this vast concentrated power Professor Dexter was a little awed and a little appalled at the responsibility which had suddenly devolved upon him, naturally enough with this culmination of a project which he had cherished for months. Briefly this had been to gather into one cohesive whole the many particles of the precious substance scattered over the world for the purpose of elaborate experiments as to its motive power practicability. Now here it was.

Its value, based on scarcity of supply, was incalculable. Millions of dollars would not replace it. Minute portions had come from the four quarters of the globe, in each case by special messenger, and each separate grain had been heavily insured by Lloyd’s at a staggering premium. It was only after months of labour, backed by the influence of the great university of Yarvard in which he held the chair of physics, that Professor Dexter had been able to accomplish his purpose.

At least one famous name had been loaned to the proposed experiments, that of the distinguished scientist and logician, Professor Augustus S. F. X. Van Dusen — so called The Thinking Machine. The interest of this master mind in the work was a triumph for Professor Dexter, who was young and comparatively unknown. The elder scientist — The Thinking Machine — was a court of last appeal in the sciences and from the moment his connection with Professor Dexter’s plans was announced his fellows all over the world had been anxiously awaiting a first word.

Naturally the task of gathering so great a quantity of radium had not been accomplished without extensive, and sometimes sensational, newspaper comment all over the United States and Europe. It was not astonishing, therefore that news of the receipt of the final portion of the radium at Yarvard had been known in the daily press and with it a statement that Professors Van Dusen and Dexter would immediately begin their experiments.

The work was to be done in the immense laboratory at Yarvard a high-ceilinged room with roof partially of glass, and with windows set high in the walls far above the reach of curious eyes. Full preparations had been made; — the two men were to work together, and a guard was to be stationed at the single door. This door led into a smaller room, a sort of reception hall, which in turn connected with the main hallway of the building.

Now Professor Dexter was alone in the laboratory, waiting impatiently for The Thinking Machine and turning over in his mind the preliminary steps in the labour he had undertaken. Every instrument was in place, all else was put aside for these experiments, which were either to revolutionize the motive power of the world or else demonstrate the utter uselessness of radium as a practical force.

Professor Dexter’s line of thought was interrupted by the appearance of Mr. Bowen, one of the instructors of the University.

“A lady to see you, Professor,” he said as he handed him a card. “She said it was a matter of great importance to you.”

Professor Dexter glanced at the card as Mr. Bowen turned and went out through the small room into the main hallway. The name, Mme. Therese du Chastaigny, was wholly unfamiliar. Puzzled a little and perhaps impatient too, he carefully laid the steel with its burden of radium on the long table, and started out into the reception room. Almost in the door he stumbled against something, recovered his equilibrium with an effort and brought up with an undignified jerk.

The colour mounted to his modest ears as he heard a woman laugh — a pleasant, musical, throaty sort of ripple that under other circumstances would have been agreeable. Now, being directed at his own discomfiture, it was irritating, and the Professor’s face tingled a little as a tall woman arose and came towards him.

“Please pardon me,” she said contritely, but there was still a flicker of a smile upon her red lips. “It was my carelessness. I should not have placed my suit case in the door.” She lifted it easily and replaced it in that identical position. “Or perhaps,” she suggested, inquiringly, “someone else coming out might stumble as you did?”

“No,” replied the Professor, and he smiled a little through his blushes. “There is no one else in there.”

As Mme. du Chastaigny straightened up, with a rustle of skirts, to greet him Professor Dexter was somewhat surprised at her height and at the splendid lines of her figure. She was apparently of thirty years and seemed from a casual glance, to be five feet nine or ten inches tall. In addition to a certain striking indefinable beauty she was of remarkable physical power if one might judge from her poise and manner. Professor Dexter glanced at her and then at the card inquiringly.

“I have a letter of introduction to you from Mme. Curie of France,” she explained as she produced it from a tiny chatelaine bag. “Shall we go over here where the light is better?”

She handed the letter to him and together they seated themselves under one of the windows near the door into the outer hallway. Professor Dexter pulled up a light chair facing her and opened the letter. He glanced through it and then looked up with a newly kindled interest in his eyes.

“I should not have disturbed you,” Mme. du Chastaigny explained pleasantly, “had I not known it was a matter of the greatest possible interest to you.”

“Yes?” Professor Dexter nodded. “It’s radium,” she continued. “It just happens that I have in my possession practically an ounce of radium of which the world of science has never heard.”

“An ounce of radium!” repeated Professor Dexter, incredulously. “Why, Madame, you astonish, amaze me. An ounce of radium?”

He leaned further forward in his chair and waited expectantly while Mme. du Chastaigny coughed violently. The paroxysm passed after a moment.

“That is my punishment for laughing,” she explained, smilingly. “I trust you will pardon me. I have a bad throat — and it was quick retribution.”

“Yes, yes,” said the other courteously, “but this other — it’s most interesting. Please tell me about it.”

Mme. du Chastaigny made herself comfortable in the chair, cleared her throat, and began.

“It’s rather an unusual story,” she said apologetically, “but the radium came into my possession in quite a natural manner. I am English, so I speak the language, but my husband was French as my name indicates, and, he, like you, was a scientist. He was little known to the world at large, however, as he was not connected with any institution. His experiments were undertaken for amusement and gradually led to a complete absorption of his interest. We were not wealthy as Americans count it, but we were comfortably well off.

“That much for my affairs. The letter I gave you from Mme. Curie will tell you the rest as to who I am. Now when the discovery of radium was made by M. and Mme. Curie my husband began some investigations along the same line and they proved to be remarkably successful. His efforts were first directed towards producing radium, with what object, I was not aware at that time. In the course of months he made grain after grain by some process unlike that of the Curies’, and incidentally he spent practically all our little fortune. Finally he had nearly an ounce.”

“Most interesting!” commented Professor Dexter. “Please go on.”

“It happened that during the production of the last quarter of an ounce, my husband contracted an illness which later proved fatal,” Mme. du Chastaigny resumed after a slight pause, and her voice dropped. “I did not know the purpose of his experiments; I only knew what they had been and their comparative cost. On his death bed he revealed this purpose to me. Strangely enough it was identical with yours as the newspapers have announced it — that is, the practicability of radium as a motive power. He was at work on plans looking to the utilization of its power when he died but these plans were not perfected and unfortunately were in such shape as to be unintelligible to another.”

She paused and sat silent for a moment. Professor Dexter watching her face, traced a shadow of grief and sorrow there and his own big heart prompted a ready sympathy.

“And what,” he asked, “was your purpose in coming to me now?”

“I know of the efforts you have made and the difficulties you have encountered in gathering enough radium for the experiments you have in mind,” Mme. du Chastaigny continued, “and it occurred to me that what I have, which is of no possible use to me, might be sold to you or to the university. As I said, there is nearly an ounce of it. It is where I can put my hands on it, and you of course are to make the tests to prove it is what it should be.”

“Sell it?” gasped Professor Dexter. “Why, Madame, it’s impossible. The funds of the college are not so plentiful that the vast fortune necessary to purchase such a quantity would be forthcoming.”

A certain hopeful light in the face of the young woman passed and there was a quick gesture of her hands which indicated disappointment.

“You speak of a vast fortune,” she said at last. “I could not hope, of course, to realize anything like the actual value of the substance — a million perhaps? Only a few hundred thousands? Something to convert into available funds for me the fortune which has been sunk.”

There was almost an appeal in her limpid voice and Professor Dexter considered the matter deeply for several minutes as he stared out the window.

“Or perhaps,” the woman hurried on after a moment, “it might be that you need more radium for the experiments you have in hand now, and there might be some sum paid me for the use of what I have? A sort of royalty? I am willing to do anything within reason.”

Again there was a long pause. Ahead of him, with this hitherto unheard of quantity of radium available, Professor Dexter saw rosy possibilities in his chosen work. The thought gripped him more firmly as he considered it. He could see little chance of a purchase — but the use of the substance during his experiments! That might be arranged.

“Madame,” he said at last, “I want to thank you deeply for coming to me. While I can promise nothing definite I can promise that I will take up the matter with certain persons who may be able to do something for you. It’s perfectly astounding. Yes, I may say that I will do something, but I shall perhaps, require several days to bring it about. Will you grant me that time?”

Mme. du Chastaigny smiled.

“I must of course,” she said, and again she went off into a paroxysm of coughing, a distressing, hacking outburst which seemed to shake her whole body. “Of course,” she added, when the spasm passed, “I can only hope that you can do something either in purchasing or using it.”

“Could you fix a definite price for the quantity you have — that is a sale price — and another price merely for its use?” asked Professor Dexter.

“I can’t do that offhand of course, but here is my address on this card — Hotel Teutonic. I expect to remain there for a few days and you may reach me any time. Please, now please,” and again there was a pleading note in her voice, and she laid one hand on his arm, “don’t hesitate to make any offer to me. I shall be only too glad to accept it if I can.”

She arose and Professor Dexter stood beside her.

“For your information,” she went on, “I will explain that I only arrived in this country yesterday by steamer from Liverpool and my need is such that within another six months I shall be absolutely dependent upon what I may realize from the radium.”

She crossed the room, picked up the suit case and again she smiled, evidently at the recollection of Professor Dexter’s awkward stumble. Then with her burden she turned to go.

“Permit me, Madame,” suggested Professor Dexter, quickly as he reached for the bag.

“Oh no, it is quite light,” she responded easily.

There were a few commonplaces and then she went out. Gazing through the window after her Professor Dexter noted, with certain admiration in his eyes the graceful strong lines of her figure as she entered a carriage and was driven away. He stood deeply thoughtful for a minute considering the possibilities arising from her casual announcement of the existence of this unknown radium.

“If I only had that too,” he muttered as he turned and reentered his work room.

An instant later, a cry — a wild amazed shriek — came from the laboratory and Professor Dexter, with pallid face, rushed out through the reception room and flung open the door into the main hallway. Half a dozen students gathered about him and from across the hall Mr. Bowen, the instructor, appeared with startled eyes.

“The radium is gone — stolen!” gasped Professor Dexter.

The members of the little group stared at one another blankly while Professor Dexter raved impotently and ran his fingers through his hair. There were questions and conjectures; a babble was raging about him when a new figure loomed up in the picture. It was that of a small man with an enormous yellow head and an eternal petulant droop to the corners of his mouth. He had just turned a corner in the hall.

“Ah, Professor Van Dusen,” exclaimed Professor Dexter, and he seized the long, slender hand of The Thinking Machine in a frenzied grip.

“Dear me! Dear me!” complained The Thinking Machine as he sought to extract his fingers from the vice. “Don’t do that. What’s the matter?”

“The radium is gone — stolen!” Professor Dexter explained.

The Thinking Machine drew back a little and squinted aggressively into the distended eyes of his fellow scientist.

“Why that’s perfectly silly,” he said at last. “Come in, please, and tell me what happened.”

With perspiration dripping from his brow and hands atremble, Professor Dexter followed him into the reception room, whereupon The Thinking Machine turned, closed the door into the hallway and snapped the lock. Outside Mr. Bowen and the students heard the click and turned away to send the astonishing news hurtling through the great university. Inside Professor Dexter sank down on a chair with staring eyes and nervously twitching lips.

“Dear me, Dexter, are you crazy?” demanded The Thinking Machine irritably. “Compose yourself. What happened? What were the circumstances of the disappearance?”

“Come — come in here — the laboratory and see,” suggested Professor Dexter.

“Oh, never mind that now,” said the other impatiently. “Tell me what happened?”

Professor Dexter paced the length of the small room twice then sat down again, controlling himself with a perceptible effort. Then, ramblingly but completely, he told the story of Mme. du Chastaigny’s call, covering every circumstance from the time he placed the radium on the table in the laboratory until he saw her drive away in the carriage. The Thinking Machine leaned back in his chair with squint eyes upturned and slender white fingers pressed tip to tip.

“How long was she here?” he asked at the end.

“Ten minutes, I should say,” was the reply.

“Where did she sit?”

“Right where you are, facing the laboratory door.”

The Thinking Machine glanced back at the window behind him.

“And you?” he asked.

“I sat here facing her.”

“You know that she did not enter the laboratory?”

“I know it, yes,” replied Professor Dexter promptly. “No one save me has entered that laboratory today. I have taken particular pains to see that no one did. When Mr. Bowen spoke to me I had the radium in my hand. He merely opened the door, handed me her card and went right out. Of course it’s impossible that —”

“Nothing is impossible, Mr. Dexter,” blazed The Thinking Machine suddenly. “Did you at any time leave Mme. du Chastaigny in this room alone?”

“No, no,” declared Dexter emphatically. “I was looking at her every moment she was here; I did not put the radium out of my hand until Mr. Bowen was out of this room and in the hallway there. I then came into this room and met her.”

For several minutes The Thinking Machine sat perfectly silent, squinting upward while Professor Dexter gazed into the inscrutable face anxiously.

“I hope,” ventured the Professor at last, “that you do not believe it was any fault of mine?”

The Thinking Machine did not say.

“What sort of a voice has Mme. du Chastaigny?” he asked instead.

The Professor blinked a little in bewilderment.

“An ordinary voice — the low voice of a woman of education and refinement,” he replied.

“Did she raise it at any time while talking?”

“No.”

“Perhaps she sneezed or coughed while talking to you?”

Unadulterated astonishment was written on Professor Dexter’s face.

“She coughed, yes, violently,” he replied.

“Ah!” exclaimed The Thinking Machine and there was a flash of comprehension in the narrow blue eyes. “Twice, I suppose?”

Professor Dexter was staring at the scientist blankly.

“Yes, twice,” he responded.

“Anything else?”

“Well, she laughed I think.”

“What was the occasion of her laughter?”

“I stumbled over a suit case she had set down by the laboratory door there.”

The Thinking Machine absorbed that without evidence of emotion, then reached for the letter of introduction which Mme. du Chastaigny had given to Professor Dexter and which he still carried crumpled up in his hand. It was a short note, just a few lines in French, explaining that Mme. du Chastaigny desired to see Professor Dexter on a matter of importance.

“Do you happen to know Mme. Curie’s handwriting?” asked The Thinking Machine after............