“I shall have to have your promise also on that point, Professor. For one year you will have to keep your discovery to yourself. That will be sufficient for my revenge.”
He realised that had he made no proviso of that sort it would have been enough to raise the other’s suspicions, for Professor Goodman was no fool. He also realised that if he made the period too long the other’s inherent pigheadedness might tempt him to refuse. So he compromised on a year, and to his intense relief it looked as if the old man was inclined to consider it favourably. He still sat motionless, but his brow was wrinkled in thought, and he drummed incessantly with his fingers on the arms of his chair.
“One year,” he said at length. “For I warn you, sir, that all the Petersons in the world will not prevent me publishing my discovery then.”
“One year will be sufficient,” said Mr. Robinson quietly.
“And will you on your side,” continued the Professor, “promise not to publish it before that date?”
Mr. Robinson concealed a smile.
“I undoubtedly will promise that,” he answered.
“And the instant you possess the secret I may go to my wife?”
Mr. Robinson’s pulse was beating a little quicker than normal. Could it be that he had succeeded in bluffing him?
“As soon as Peterson knows that the secret of the process is mine—and that will be very soon—you may go. Before that it would not be safe.”
“And if I refuse?”
For a moment or two Mr. Robinson did not reply; he seemed to be weighing his words with care.
“Need we discuss that, Professor?” he said at length. “I have already told you the main—almost the sole—object of my life: revenge on this man Peterson. Rightly or wrongly, I have decided that this is my opportunity for obtaining it. I have gone to an immensity of trouble and risk to achieve my object, and though, as I said, I have no quarrel with you, yet, Professor, you are an essential part of my scheme. Without you I must fail; I make no bones about it. And I do not want to fail. So should you still refuse, your wife will go on thinking herself a widow until you change your mind. It rests with you and you alone.”
His eyes, shrewd and penetrating, searched the old man’s face. Had he said enough, or had he said too much? Like an open book he read the other’s mind: saw doubt, indecision, despair, succeed one another in rapid succession. And then suddenly he almost stopped breathing. For the Professor had risen to his feet, and Mr. Robinson knew that one way or the other he had come to a decision.
“Very well, sir,” said the old man wearily. “I give in. It seems that the only way of setting my poor wife’s mind at rest as soon as possible is for me to trust you. I will tell you my process.”
Mr. Robinson drew in his breath in a little whistling hiss, but his voice was quite steady as he answered.
“You have decided very wisely,” he remarked. “And since there is no time like the present, I think we will have a bottle of champagne and some sandwiches to fortify us, and then get on with the experiment at once.”
“As you will,” said the Professor. “And then perhaps tomorrow you will let me go.”
Mr. Robinson glanced at his watch.
“Today, Professor,” he remarked jovially. “It is past midnight. And I can promise you that should your experiment succeed, you will leave this house today.”
He watched the champagne bring back some colour to the other’s cheeks, and then he produced his notebook.
“To save time,” he said, “I propose to write down the name of each salt as you take it, and the amount you use. Does it make any difference in what order the salts are mixed?”
“None whatever,” answered the Professor. “Provided they are all mixed properly. No chemical reaction takes place until the heat is applied.”
“And to make it perfectly certain, you had better give me the formula for each salt at the same time,” continued Mr. Robinson.
At first the old man’s fingers trembled so much that he could hardly use the balance, but Mr. Robinson betrayed no impatience. And after a while the enthusiasm of the scientist supplanted everything else, and the Professor became absorbed in his task. Entry after entry was made in Mr. Robinson’s neat handwriting, and gradually the look of triumph deepened in his eyes. Success had come at last.
Of pity for the poor old man opposite he felt no trace; pity was a word unknown in his vocabulary. And so for an hour in the silent house the murderer and his victim worked on steadily, until, at length, the last salt was mixed, the last entry made. The secret was in Mr. Robinson’s possession. Not for another four hours would he be absolutely certain; the test of the electric furnace would furnish the only conclusive proof. But short of that he felt as sure as a man may feel that there had been no mistake this time, and his eyes were gleaming as he rose from the table.
“Excellent, my dear Professor,” he murmured. “You have been lucidity itself. Now all that remains is to start up our current and await results.”
“The results will be there,” answered the other. “That I know.”
He opened the furnace door and placed the retort inside; then, switching on the current, he sank wearily into his chair.
“You don’t think it will be long, do you, before you can convince this man Peterson?” he said with a pathetic sort of eagerness.
“I can assure you that it won’t be,” returned the other, with an enigmatic smile. “I
